<?xml version="1.0" encoding="us-ascii"?>
<!-- DFIN ActiveDisclosure(SM) XBRL Linkbase Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2022-07-27T00:04:50.8584910+00:00 -->
<!-- Version            : 5.0.1.747 -->
<!-- Package ID         : ecd6d60c3f3f408f8688a4767057c3e2 -->
<!-- Copyright (c) 2022 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" arcroleURI="http://xbrl.org/int/dim/arcrole/all" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" />
  <link:arcroleRef xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" />
  <link:roleRef xlink:type="simple" xlink:href="alks-20220630.xsd#TemplateLink" roleURI="http://www.alkermes.com/20220630/role/TemplateLink" />
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSSINCOMEUnaudited" xlink:href="alks-20220630.xsd#Role_StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSSINCOMEUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSSINCOMEUnaudited">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:type="locator" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="locator" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAbstract" xlink:type="locator" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareDiluted" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareDiluted" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareBasic" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareBasic" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EarningsPerShareAbstract" xlink:type="locator" xlink:label="us-gaap_EarningsPerShareAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:type="locator" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:type="locator" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpense" xlink:type="locator" xlink:label="us-gaap_NonoperatingIncomeExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:type="locator" xlink:label="us-gaap_OtherNonoperatingIncomeExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationAsset1" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationAsset1" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpense" xlink:type="locator" xlink:label="us-gaap_InterestExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentIncomeInterest" xlink:type="locator" xlink:label="us-gaap_InvestmentIncomeInterest" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:type="locator" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OperatingIncomeLoss" xlink:type="locator" xlink:label="us-gaap_OperatingIncomeLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpenses" xlink:type="locator" xlink:label="us-gaap_CostsAndExpenses" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:type="locator" xlink:label="us-gaap_AmortizationOfIntangibleAssets" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:type="locator" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfGoodsAndServicesSold" xlink:type="locator" xlink:label="us-gaap_CostOfGoodsAndServicesSold" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostsAndExpensesAbstract" xlink:type="locator" xlink:label="us-gaap_CostsAndExpensesAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueAbstract" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueAbstract" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ResearchAndDevelopmentMember" xlink:type="locator" xlink:label="alks_ResearchAndDevelopmentMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LicenseMember" xlink:type="locator" xlink:label="us-gaap_LicenseMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ManufacturedProductAndRoyaltyMember" xlink:type="locator" xlink:label="alks_ManufacturedProductAndRoyaltyMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductMember" xlink:type="locator" xlink:label="us-gaap_ProductMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10170.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain_2" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ManufacturedProductAndRoyaltyMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_LicenseMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ResearchAndDevelopmentMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueAbstract" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueAbstract" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_CostsAndExpensesAbstract" order="11020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_CostOfGoodsAndServicesSold" order="11180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_ResearchAndDevelopmentExpense" order="11260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpense" order="11340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_AmortizationOfIntangibleAssets" order="11420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_CostsAndExpensesAbstract" xlink:to="us-gaap_CostsAndExpenses" order="11500.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OperatingIncomeLoss" order="11580.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract" order="11660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InvestmentIncomeInterest" order="11820.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_InterestExpense" order="11900.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationAsset1" order="11980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherNonoperatingIncomeExpense" order="12060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NonoperatingIncomeExpense" order="12140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" order="12220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_IncomeTaxExpenseBenefit" order="12300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" order="12380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_EarningsPerShareAbstract" order="12460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareBasic" order="12620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareDiluted" order="12700.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" order="12780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" order="12940.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" order="13020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ComprehensiveIncomeNetOfTaxAbstract" order="13100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ComprehensiveIncomeNetOfTaxAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" order="13340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ComprehensiveIncomeNetOfTaxAbstract" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax" order="13420.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITYUnaudited" xlink:href="alks-20220630.xsd#Role_StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITYUnaudited" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/StatementCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITYUnaudited">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" xlink:type="locator" xlink:label="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:type="locator" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsShares" xlink:type="locator" xlink:label="alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsShares" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValue" xlink:type="locator" xlink:label="alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValue" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" xlink:type="locator" xlink:label="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SharesOutstanding" xlink:type="locator" xlink:label="us-gaap_SharesOutstanding" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StockholdersEquity" xlink:type="locator" xlink:label="us-gaap_StockholdersEquity" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TreasuryStockMember" xlink:type="locator" xlink:label="us-gaap_TreasuryStockMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RetainedEarningsMember" xlink:type="locator" xlink:label="us-gaap_RetainedEarningsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:type="locator" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:type="locator" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CommonStockMember" xlink:type="locator" xlink:label="us-gaap_CommonStockMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityComponentDomain" xlink:type="locator" xlink:label="us-gaap_EquityComponentDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementEquityComponentsAxis" xlink:type="locator" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_TreasuryStockMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" order="10420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesOutstanding" order="10440.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation" order="10600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsValue" order="10780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="alks_ReceiptOfCompanyStockForExerciseOfStockOptionsOrToSatisfyMinimumTaxWithholdingObligationsRelatedToStockBasedAwardsShares" order="10800.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" order="10960.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax" order="11140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" order="11320.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersTables" xlink:href="alks-20220630.xsd#Role_DisclosureRevenueFromContractsWithCustomersTables" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersTables">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTableTextBlock" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueTableTextBlock" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ManufacturedProductAndRoyaltyMember" xlink:type="locator" xlink:label="alks_ManufacturedProductAndRoyaltyMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductMember" xlink:type="locator" xlink:label="us-gaap_ProductMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementTable" xlink:type="locator" xlink:label="us-gaap_StatementTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_StatementLineItems" xlink:type="locator" xlink:label="us-gaap_StatementLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_StatementTable" xlink:to="srt_ProductOrServiceAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ManufacturedProductAndRoyaltyMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTableTextBlock" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_ContractWithCustomerAssetAndLiabilityTableTextBlock" order="10370.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersScheduleOfDisaggregationOfRevenueDetails" xlink:href="alks-20220630.xsd#Role_DisclosureRevenueFromContractsWithCustomersScheduleOfDisaggregationOfRevenueDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersScheduleOfDisaggregationOfRevenueDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProductMember" xlink:type="locator" xlink:label="us-gaap_ProductMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LYBALVIMember" xlink:type="locator" xlink:label="alks_LYBALVIMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_AristadaAndAristadaInitioMember" xlink:type="locator" xlink:label="alks_AristadaAndAristadaInitioMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_VivitrolMember" xlink:type="locator" xlink:label="alks_VivitrolMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_VivitrolMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_AristadaAndAristadaInitioMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_LYBALVIMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_ProductMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" order="10180.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersScheduleOfManufacturingAndRoyaltyRevenuesDetails" xlink:href="alks-20220630.xsd#Role_DisclosureRevenueFromContractsWithCustomersScheduleOfManufacturingAndRoyaltyRevenuesDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersScheduleOfManufacturingAndRoyaltyRevenuesDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" xlink:type="locator" xlink:label="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" />
    <link:loc xlink:href="alks-20220630.xsd#alks_OtherProductsAndServicesMember" xlink:type="locator" xlink:label="alks_OtherProductsAndServicesMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_RISPERDALCONSTAMember" xlink:type="locator" xlink:label="alks_RISPERDALCONSTAMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_VumerityMember" xlink:type="locator" xlink:label="alks_VumerityMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongActingINVEGAProductsMember" xlink:type="locator" xlink:label="alks_LongActingINVEGAProductsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="locator" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:type="locator" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TypeOfArrangementAxis" xlink:type="locator" xlink:label="us-gaap_TypeOfArrangementAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ManufacturedProductAndRoyaltyMember" xlink:type="locator" xlink:label="alks_ManufacturedProductAndRoyaltyMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RoyaltyMember" xlink:type="locator" xlink:label="us-gaap_RoyaltyMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ManufacturingRevenueMember" xlink:type="locator" xlink:label="alks_ManufacturingRevenueMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ManufacturingRevenueMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="us-gaap_RoyaltyMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ManufacturedProductAndRoyaltyMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="us-gaap_TypeOfArrangementAxis" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_2" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="alks_LongActingINVEGAProductsMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="alks_VumerityMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="alks_RISPERDALCONSTAMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="alks_OtherProductsAndServicesMember" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax" order="10620.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersAdditionalInformationDetails" xlink:href="alks-20220630.xsd#Role_DisclosureRevenueFromContractsWithCustomersAdditionalInformationDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureRevenueFromContractsWithCustomersAdditionalInformationDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerLiability" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerLiability" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ConsiderationExpectedToReceiveYear" xlink:type="locator" xlink:label="alks_ConsiderationExpectedToReceiveYear" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ManufacturingProcessPeriod" xlink:type="locator" xlink:label="alks_ManufacturingProcessPeriod" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ContractWithCustomerAssetNetCurrent" xlink:type="locator" xlink:label="us-gaap_ContractWithCustomerAssetNetCurrent" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherNoncurrentLiabilitiesMember" xlink:type="locator" xlink:label="us-gaap_OtherNoncurrentLiabilitiesMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ContractLiabilitiesMember" xlink:type="locator" xlink:label="alks_ContractLiabilitiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_BiogenMember" xlink:type="locator" xlink:label="alks_BiogenMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain" xlink:type="locator" xlink:label="srt_NameOfMajorCustomerDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_NameOfMajorCustomerDomain" xlink:type="locator" xlink:label="srt_NameOfMajorCustomerDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MajorCustomersAxis" xlink:type="locator" xlink:label="srt_MajorCustomersAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_VumerityMember" xlink:type="locator" xlink:label="alks_VumerityMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueTable" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DisaggregationOfRevenueLineItems" xlink:type="locator" xlink:label="us-gaap_DisaggregationOfRevenueLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_DisaggregationOfRevenueTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_RangeAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_ProductOrServiceAxis" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_VumerityMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="srt_MajorCustomersAxis" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain_2" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_MajorCustomersAxis" xlink:to="srt_NameOfMajorCustomerDomain" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_NameOfMajorCustomerDomain" xlink:to="alks_BiogenMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DisaggregationOfRevenueTable" xlink:to="us-gaap_BalanceSheetLocationAxis" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain_2" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" order="10350.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="alks_ContractLiabilitiesMember" order="10370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherNoncurrentLiabilitiesMember" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_ContractWithCustomerAssetNetCurrent" order="10420.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="alks_ManufacturingProcessPeriod" order="10540.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="alks_ConsiderationExpectedToReceiveYear" order="10600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DisaggregationOfRevenueLineItems" xlink:to="us-gaap_ContractWithCustomerLiability" order="10690.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureInvestmentsScheduleOfInvestmentsDetails" xlink:href="alks-20220630.xsd#Role_DisclosureInvestmentsScheduleOfInvestmentsDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureInvestmentsScheduleOfInvestmentsDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShortTermInvestments" xlink:type="locator" xlink:label="us-gaap_ShortTermInvestments" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" xlink:type="locator" xlink:label="alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" xlink:type="locator" xlink:label="alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ShortTermInvestmentSecuritiesUnrealizedGainLoss" xlink:type="locator" xlink:label="alks_ShortTermInvestmentSecuritiesUnrealizedGainLoss" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ShortTermInvestmentAmortizedCost" xlink:type="locator" xlink:label="alks_ShortTermInvestmentAmortizedCost" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShortTermInvestmentsAbstract" xlink:type="locator" xlink:label="us-gaap_ShortTermInvestmentsAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_InvestmentsFairValueDisclosure" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MarketableSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses" xlink:type="locator" xlink:label="alks_MarketableSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MarketableSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" xlink:type="locator" xlink:label="alks_MarketableSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MarketableInvestmentsSecuritiesUnrealizedGainLoss" xlink:type="locator" xlink:label="alks_MarketableInvestmentsSecuritiesUnrealizedGainLoss" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MarketableSecuritiesAtAmortizedCost" xlink:type="locator" xlink:label="alks_MarketableSecuritiesAtAmortizedCost" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_MarketableSecuritiesAbstract" xlink:type="locator" xlink:label="us-gaap_MarketableSecuritiesAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermInvestments" xlink:type="locator" xlink:label="us-gaap_LongTermInvestments" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" xlink:type="locator" xlink:label="alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" xlink:type="locator" xlink:label="alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongTermInvestmentSecuritiesUnrealizedGainLoss" xlink:type="locator" xlink:label="alks_LongTermInvestmentSecuritiesUnrealizedGainLoss" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongTermInvestmentAmortizedCost" xlink:type="locator" xlink:label="alks_LongTermInvestmentAmortizedCost" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermInvestmentsAbstract" xlink:type="locator" xlink:label="us-gaap_LongTermInvestmentsAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesFairValue" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesFairValue" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:type="locator" xlink:label="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesAbstract" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CertificatesOfDepositMember" xlink:type="locator" xlink:label="us-gaap_CertificatesOfDepositMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:type="locator" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:type="locator" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_ForeignGovernmentDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:type="locator" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FinancialInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_LongTermInvestmentsMember" xlink:type="locator" xlink:label="alks_LongTermInvestmentsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShortTermInvestmentsMember" xlink:type="locator" xlink:label="us-gaap_ShortTermInvestmentsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:type="locator" xlink:label="us-gaap_InvestmentTypeCategorizationMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:type="locator" xlink:label="us-gaap_InvestmentTypeCategorizationMember_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentTypeAxis" xlink:type="locator" xlink:label="us-gaap_InvestmentTypeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentHoldingsTable" xlink:type="locator" xlink:label="us-gaap_InvestmentHoldingsTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentHoldingsLineItems" xlink:type="locator" xlink:label="us-gaap_InvestmentHoldingsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_InvestmentHoldingsTable" order="10210.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_InvestmentTypeAxis" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember_2" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_InvestmentTypeAxis" xlink:to="us-gaap_InvestmentTypeCategorizationMember" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="us-gaap_ShortTermInvestmentsMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentTypeCategorizationMember" xlink:to="alks_LongTermInvestmentsMember" order="10370.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_FinancialInstrumentAxis" order="10600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2" order="10610.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="10630.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" order="10650.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" order="10670.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="us-gaap_ForeignGovernmentDebtSecuritiesMember" order="10690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_CashAndCashEquivalentsAxis" order="10960.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_CashAndCashEquivalentsAxis" xlink:to="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_2" order="10970.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_CashAndCashEquivalentsAxis" xlink:to="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" order="10990.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="us-gaap_CertificatesOfDepositMember" order="11010.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesAbstract" order="11060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis" order="11700.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" order="12020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" order="12340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" order="12660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AvailableForSaleSecuritiesAbstract" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="12980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" order="13330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesAmortizedCostBeforeOtherThanTemporaryImpairment" order="13450.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain" order="13510.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss" order="13570.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss" order="13630.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_HeldToMaturitySecuritiesParentheticalDisclosureAbstract" xlink:to="us-gaap_HeldToMaturitySecuritiesFairValue" order="13690.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_LongTermInvestmentsAbstract" order="13780.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongTermInvestmentsAbstract" xlink:to="alks_LongTermInvestmentAmortizedCost" order="13860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongTermInvestmentsAbstract" xlink:to="alks_LongTermInvestmentSecuritiesUnrealizedGainLoss" order="13900.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongTermInvestmentsAbstract" xlink:to="alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" order="13940.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongTermInvestmentsAbstract" xlink:to="alks_LongTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" order="13980.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongTermInvestmentsAbstract" xlink:to="us-gaap_LongTermInvestments" order="14020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_MarketableSecuritiesAbstract" order="14090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MarketableSecuritiesAbstract" xlink:to="alks_MarketableSecuritiesAtAmortizedCost" order="14170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MarketableSecuritiesAbstract" xlink:to="alks_MarketableInvestmentsSecuritiesUnrealizedGainLoss" order="14210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MarketableSecuritiesAbstract" xlink:to="alks_MarketableSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" order="14250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MarketableSecuritiesAbstract" xlink:to="alks_MarketableSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses" order="14290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_MarketableSecuritiesAbstract" xlink:to="us-gaap_InvestmentsFairValueDisclosure" order="14330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_ShortTermInvestmentsAbstract" order="14400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="alks_ShortTermInvestmentAmortizedCost" order="14480.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="alks_ShortTermInvestmentSecuritiesUnrealizedGainLoss" order="14520.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses" order="14560.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="alks_ShortTermInvestmentSecuritiesContinuousUnrealizedLossPositionMoreThan12MonthsAggregateLosses" order="14600.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_ShortTermInvestmentsAbstract" xlink:to="us-gaap_ShortTermInvestments" order="14640.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureInvestmentsAdditionalInformationDetails" xlink:href="alks-20220630.xsd#Role_DisclosureInvestmentsAdditionalInformationDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureInvestmentsAdditionalInformationDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestments" xlink:type="locator" xlink:label="us-gaap_EquityMethodInvestments" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ReturnOfInvestments" xlink:type="locator" xlink:label="alks_ReturnOfInvestments" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeLossFromEquityMethodInvestments" xlink:type="locator" xlink:label="us-gaap_IncomeLossFromEquityMethodInvestments" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EscrowDeposit" xlink:type="locator" xlink:label="us-gaap_EscrowDeposit" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ProceedsFromSaleOfEquityMethodInvestments" xlink:type="locator" xlink:label="us-gaap_ProceedsFromSaleOfEquityMethodInvestments" />
    <link:loc xlink:href="alks-20220630.xsd#alks_NumberOfPortfolioSold" xlink:type="locator" xlink:label="alks_NumberOfPortfolioSold" />
    <link:loc xlink:href="alks-20220630.xsd#alks_EquityMethodCommitment" xlink:type="locator" xlink:label="alks_EquityMethodCommitment" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FundingCommitmentAsPercentageOfPartnershipsFunding" xlink:type="locator" xlink:label="alks_FundingCommitmentAsPercentageOfPartnershipsFunding" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:type="locator" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentMaturityDate" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentFaceAmount" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" xlink:type="locator" xlink:label="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" xlink:type="locator" xlink:label="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherAssetsMember" xlink:type="locator" xlink:label="us-gaap_OtherAssetsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationDomain" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BalanceSheetLocationAxis" xlink:type="locator" xlink:label="us-gaap_BalanceSheetLocationAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherExpenseMember" xlink:type="locator" xlink:label="us-gaap_OtherExpenseMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FountainHealthcarePartnersIiLpOfIrelandMember" xlink:type="locator" xlink:label="alks_FountainHealthcarePartnersIiLpOfIrelandMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvesteeMember" xlink:type="locator" xlink:label="us-gaap_InvesteeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:type="locator" xlink:label="us-gaap_RelatedPartyDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyDomain" xlink:type="locator" xlink:label="us-gaap_RelatedPartyDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:type="locator" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ConvertiblePromissoryNotesMember" xlink:type="locator" xlink:label="alks_ConvertiblePromissoryNotesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentNameDomain" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentNameDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentAxis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_SynchronicityPharmaIncMember" xlink:type="locator" xlink:label="alks_SynchronicityPharmaIncMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:type="locator" xlink:label="srt_EquityMethodInvesteeNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_EquityMethodInvesteeNameDomain" xlink:type="locator" xlink:label="srt_EquityMethodInvesteeNameDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:type="locator" xlink:label="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_OtherOperatingIncomeExpenseMember" xlink:type="locator" xlink:label="us-gaap_OtherOperatingIncomeExpenseMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentHoldingsTable" xlink:type="locator" xlink:label="us-gaap_InvestmentHoldingsTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InvestmentHoldingsLineItems" xlink:type="locator" xlink:label="us-gaap_InvestmentHoldingsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_InvestmentHoldingsTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_IncomeStatementLocationAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_OtherOperatingIncomeExpenseMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain_2" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="srt_EquityMethodInvesteeNameDomain" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="alks_SynchronicityPharmaIncMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_DebtInstrumentAxis" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain_2" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="alks_ConvertiblePromissoryNotesMember" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyDomain_2" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyDomain" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_InvesteeMember" order="10330.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="srt_RangeAxis" order="10380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10410.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10430.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10450.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_EquityMethodInvesteeNameDomain" xlink:to="alks_FountainHealthcarePartnersIiLpOfIrelandMember" order="10510.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_OtherExpenseMember" order="10670.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_InvestmentHoldingsTable" xlink:to="us-gaap_BalanceSheetLocationAxis" order="10680.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_BalanceSheetLocationAxis" xlink:to="us-gaap_BalanceSheetLocationDomain" order="10710.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_BalanceSheetLocationDomain" xlink:to="us-gaap_OtherAssetsMember" order="10730.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPosition" order="10820.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_EquityMethodInvestmentOtherThanTemporaryImpairment" order="10860.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_DebtInstrumentFaceAmount" order="10930.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_DebtInstrumentMaturityDate" order="10950.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_EquityMethodInvestmentOwnershipPercentage" order="10970.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="alks_FundingCommitmentAsPercentageOfPartnershipsFunding" order="11020.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="alks_EquityMethodCommitment" order="11040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="alks_NumberOfPortfolioSold" order="11090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_ProceedsFromSaleOfEquityMethodInvestments" order="11130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_EscrowDeposit" order="11210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_IncomeLossFromEquityMethodInvestments" order="11250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="alks_ReturnOfInvestments" order="11290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_InvestmentHoldingsLineItems" xlink:to="us-gaap_EquityMethodInvestments" order="11330.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueSummaryOfCompanySAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails" xlink:href="alks-20220630.xsd#Role_DisclosureFairValueSummaryOfCompanySAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueSummaryOfCompanySAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AssetsFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_AssetsFairValueDisclosure" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationAsset" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAsset" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities" xlink:type="locator" xlink:label="us-gaap_AvailableForSaleSecuritiesDebtSecurities" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure" xlink:type="locator" xlink:label="us-gaap_CashAndCashEquivalentsFairValueDisclosure" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel3Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel2Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel2Member" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueInputsLevel1Member" xlink:type="locator" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ForeignGovernmentDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_ForeignGovernmentDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CorporateDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_CorporateDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember" xlink:type="locator" xlink:label="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueByAssetClassAxis" xlink:type="locator" xlink:label="us-gaap_FairValueByAssetClassAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" order="10060.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByAssetClassAxis" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_2" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByAssetClassAxis" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="us-gaap_USGovernmentAgenciesDebtSecuritiesMember" order="10140.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="us-gaap_CorporateDebtSecuritiesMember" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain" xlink:to="us-gaap_ForeignGovernmentDebtSecuritiesMember" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_2" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" order="10310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain_2" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" order="10360.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel2Member" order="10380.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" order="10400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_CashAndCashEquivalentsFairValueDisclosure" order="10750.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AvailableForSaleSecuritiesDebtSecurities" order="10830.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAsset" order="11070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_AssetsFairValueDisclosure" order="11150.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueAdditionalInformationDetails" xlink:href="alks-20220630.xsd#Role_DisclosureFairValueAdditionalInformationDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueAdditionalInformationDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentFairValue" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentFairValue" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationAssetNoncurrent" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAssetNoncurrent" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationAssetCurrent" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAssetCurrent" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BusinessCombinationContingentConsiderationAsset" xlink:type="locator" xlink:label="us-gaap_BusinessCombinationContingentConsiderationAsset" />
    <link:loc xlink:href="alks-20220630.xsd#alks_PercentageOfDiscountRecoveryRate" xlink:type="locator" xlink:label="alks_PercentageOfDiscountRecoveryRate" />
    <link:loc xlink:href="alks-20220630.xsd#alks_WeightingPercentageOfDefaultOnObligations" xlink:type="locator" xlink:label="alks_WeightingPercentageOfDefaultOnObligations" />
    <link:loc xlink:href="alks-20220630.xsd#alks_PercentageOfReductionInWorkforcePlanned" xlink:type="locator" xlink:label="alks_PercentageOfReductionInWorkforcePlanned" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MilestonePaymentsReceivable" xlink:type="locator" xlink:label="alks_MilestonePaymentsReceivable" />
    <link:loc xlink:href="alks-20220630.xsd#alks_NumberOfEqualAnnualInstallmentsMilestonePayment" xlink:type="locator" xlink:label="alks_NumberOfEqualAnnualInstallmentsMilestonePayment" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FutureMilestonesReceivableBetween2022And2027" xlink:type="locator" xlink:label="alks_FutureMilestonesReceivableBetween2022And2027" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MilestonePaymentsReceived" xlink:type="locator" xlink:label="alks_MilestonePaymentsReceived" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelTwoToLevelOne" xlink:type="locator" xlink:label="alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelTwoToLevelOne" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelOneToLevelTwo" xlink:type="locator" xlink:label="alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelOneToLevelTwo" />
    <link:loc xlink:href="alks-20220630.xsd#alks_TwentyTwentySixTermLoansMember" xlink:type="locator" xlink:label="alks_TwentyTwentySixTermLoansMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_BaudaxBioIncMember" xlink:type="locator" xlink:label="alks_BaudaxBioIncMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:type="locator" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:type="locator" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis" xlink:type="locator" xlink:label="srt_CounterpartyNameAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:type="locator" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:type="locator" xlink:label="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="srt_CounterpartyNameAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="alks_BaudaxBioIncMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="srt_RangeAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable" xlink:to="us-gaap_LongtermDebtTypeAxis" order="10240.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain_2" order="10250.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain" order="10270.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongtermDebtTypeDomain" xlink:to="alks_TwentyTwentySixTermLoansMember" order="10290.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelOneToLevelTwo" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_FairValueRecurringBasisAssetsOrLiabilitiesTransfersBetweenLevelTwoToLevelOne" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_MilestonePaymentsReceived" order="10390.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_FutureMilestonesReceivableBetween2022And2027" order="10430.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_NumberOfEqualAnnualInstallmentsMilestonePayment" order="10470.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_MilestonePaymentsReceivable" order="10550.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_PercentageOfReductionInWorkforcePlanned" order="10620.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_WeightingPercentageOfDefaultOnObligations" order="10700.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="alks_PercentageOfDiscountRecoveryRate" order="10720.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAsset" order="10770.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAssetCurrent" order="10810.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_BusinessCombinationContingentConsiderationAssetNoncurrent" order="10850.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems" xlink:to="us-gaap_DebtInstrumentFairValue" order="10920.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueRollforwardOfFairValueOfAssetsDeterminedUsingLevel3InputsDetails" xlink:href="alks-20220630.xsd#Role_DisclosureFairValueRollforwardOfFairValueOfAssetsDeterminedUsingLevel3InputsDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureFairValueRollforwardOfFairValueOfAssetsDeterminedUsingLevel3InputsDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" xlink:type="locator" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FairValueOfContingentConsiderationMember" xlink:type="locator" xlink:label="alks_FairValueOfContingentConsiderationMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:type="locator" xlink:label="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable" xlink:to="us-gaap_IncomeStatementLocationAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="alks_FairValueOfContingentConsiderationMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems" xlink:to="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncomeLoss" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements" order="10240.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosurePropertyPlantAndEquipmentScheduleOfPropertyPlantAndEquipmentDetails" xlink:href="alks-20220630.xsd#Role_DisclosurePropertyPlantAndEquipmentScheduleOfPropertyPlantAndEquipmentDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosurePropertyPlantAndEquipmentScheduleOfPropertyPlantAndEquipmentDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:type="locator" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ConstructionInProgressMember" xlink:type="locator" xlink:label="us-gaap_ConstructionInProgressMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LeaseholdImprovementsMember" xlink:type="locator" xlink:label="us-gaap_LeaseholdImprovementsMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_FurnitureFixtureAndEquipmentMember" xlink:type="locator" xlink:label="alks_FurnitureFixtureAndEquipmentMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_BuildingAndBuildingImprovementsMember" xlink:type="locator" xlink:label="us-gaap_BuildingAndBuildingImprovementsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LandMember" xlink:type="locator" xlink:label="us-gaap_LandMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentTypeDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentByTypeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_PropertyPlantAndEquipmentLineItems" xlink:type="locator" xlink:label="us-gaap_PropertyPlantAndEquipmentLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" order="10030.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfPropertyPlantAndEquipmentTable" xlink:to="us-gaap_PropertyPlantAndEquipmentByTypeAxis" order="10060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain_2" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:to="us-gaap_PropertyPlantAndEquipmentTypeDomain" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_LandMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_BuildingAndBuildingImprovementsMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="alks_FurnitureFixtureAndEquipmentMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_LeaseholdImprovementsMember" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:to="us-gaap_ConstructionInProgressMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentGross" order="10220.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" order="10460.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_PropertyPlantAndEquipmentLineItems" xlink:to="us-gaap_PropertyPlantAndEquipmentNet" order="10500.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsScheduleOfGoodwillAndIntangibleAssetsDetails" xlink:href="alks-20220630.xsd#Role_DisclosureGoodwillAndIntangibleAssetsScheduleOfGoodwillAndIntangibleAssetsDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsScheduleOfGoodwillAndIntangibleAssetsDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_Goodwill" xlink:type="locator" xlink:label="us-gaap_Goodwill" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_GoodwillGross" xlink:type="locator" xlink:label="us-gaap_GoodwillGross" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MaximumMember" xlink:type="locator" xlink:label="srt_MaximumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_MinimumMember" xlink:type="locator" xlink:label="srt_MinimumMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeMember" xlink:type="locator" xlink:label="srt_RangeMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RangeAxis" xlink:type="locator" xlink:label="srt_RangeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IntellectualPropertyMember" xlink:type="locator" xlink:label="us-gaap_IntellectualPropertyMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LicensingAgreementsMember" xlink:type="locator" xlink:label="us-gaap_LicensingAgreementsMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:type="locator" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_2" order="10050.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_LicensingAgreementsMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_IntellectualPropertyMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable" xlink:to="srt_RangeAxis" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" order="10190.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_GoodwillGross" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_Goodwill" order="10400.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" order="10590.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife" order="10950.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross" order="11130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" order="11310.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNetAbstract" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet" order="11490.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureAccountsPayableAndAccruedExpensesSummaryOfCurrentProvisionForSalesDiscountsAllowancesAndReservesDetails" xlink:href="alks-20220630.xsd#Role_DisclosureAccountsPayableAndAccruedExpensesSummaryOfCurrentProvisionForSalesDiscountsAllowancesAndReservesDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureAccountsPayableAndAccruedExpensesSummaryOfCurrentProvisionForSalesDiscountsAllowancesAndReservesDetails">
    <link:loc xlink:href="alks-20220630.xsd#alks_AccruedSalesDiscountsAllowancesAndReserves" xlink:type="locator" xlink:label="alks_AccruedSalesDiscountsAllowancesAndReserves" />
    <link:loc xlink:href="alks-20220630.xsd#alks_OtherMember" xlink:type="locator" xlink:label="alks_OtherMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MedicarePartDMember" xlink:type="locator" xlink:label="alks_MedicarePartDMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_ProductDiscountsMember" xlink:type="locator" xlink:label="alks_ProductDiscountsMember" />
    <link:loc xlink:href="alks-20220630.xsd#alks_MedicaidRebateMember" xlink:type="locator" xlink:label="alks_MedicaidRebateMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductsAndServicesDomain" xlink:type="locator" xlink:label="srt_ProductsAndServicesDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_ProductOrServiceAxis" xlink:type="locator" xlink:label="srt_ProductOrServiceAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_AccountsPayableAndAccruedExpensesTable" xlink:type="locator" xlink:label="alks_AccountsPayableAndAccruedExpensesTable" />
    <link:loc xlink:href="alks-20220630.xsd#alks_AccountsPayableAndAccruedExpensesLineItems" xlink:type="locator" xlink:label="alks_AccountsPayableAndAccruedExpensesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="alks_AccountsPayableAndAccruedExpensesLineItems" xlink:to="alks_AccountsPayableAndAccruedExpensesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="alks_AccountsPayableAndAccruedExpensesTable" xlink:to="srt_ProductOrServiceAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_ProductOrServiceAxis" xlink:to="srt_ProductsAndServicesDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_MedicaidRebateMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_ProductDiscountsMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_MedicarePartDMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_ProductsAndServicesDomain" xlink:to="alks_OtherMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="alks_AccountsPayableAndAccruedExpensesLineItems" xlink:to="alks_AccruedSalesDiscountsAllowancesAndReserves" order="10180.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLongTermDebtScheduleOfLongTermDebtDetails" xlink:href="alks-20220630.xsd#Role_DisclosureLongTermDebtScheduleOfLongTermDebtDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLongTermDebtScheduleOfLongTermDebtDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtNoncurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtNoncurrent" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebtCurrent" xlink:type="locator" xlink:label="us-gaap_LongTermDebtCurrent" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongTermDebt" xlink:type="locator" xlink:label="us-gaap_LongTermDebt" />
    <link:loc xlink:href="alks-20220630.xsd#alks_TwentyTwentySixTermLoansMember" xlink:type="locator" xlink:label="alks_TwentyTwentySixTermLoansMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" order="10030.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_LongtermDebtTypeAxis" order="10060.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongtermDebtTypeDomain" xlink:to="alks_TwentyTwentySixTermLoansMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebt" order="10160.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebtCurrent" order="10200.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_LongTermDebtNoncurrent" order="10240.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLongTermDebtAdditionalInformationDetails" xlink:href="alks-20220630.xsd#Role_DisclosureLongTermDebtAdditionalInformationDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLongTermDebtAdditionalInformationDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ShortTermDebtRefinancedAmount" xlink:type="locator" xlink:label="us-gaap_ShortTermDebtRefinancedAmount" />
    <link:loc xlink:href="alks-20220630.xsd#alks_DebtInstrumentIncrementalCapacitySubjectToSatisfactionOfCertainConditions" xlink:type="locator" xlink:label="alks_DebtInstrumentIncrementalCapacitySubjectToSatisfactionOfCertainConditions" />
    <link:loc xlink:href="alks-20220630.xsd#alks_DebtInstrumentVariableRateBasisFloor" xlink:type="locator" xlink:label="alks_DebtInstrumentVariableRateBasisFloor" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentMaturityDate" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentMaturityDate" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_InterestExpenseMember" xlink:type="locator" xlink:label="us-gaap_InterestExpenseMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember" xlink:type="locator" xlink:label="us-gaap_LondonInterbankOfferedRateLIBORMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:type="locator" xlink:label="us-gaap_VariableRateDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateDomain" xlink:type="locator" xlink:label="us-gaap_VariableRateDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_VariableRateAxis" xlink:type="locator" xlink:label="us-gaap_VariableRateAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_TwentyTwentySixTermLoansMember" xlink:type="locator" xlink:label="alks_TwentyTwentySixTermLoansMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeDomain" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LongtermDebtTypeAxis" xlink:type="locator" xlink:label="us-gaap_LongtermDebtTypeAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentTable" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DebtInstrumentLineItems" xlink:type="locator" xlink:label="us-gaap_DebtInstrumentLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_LongtermDebtTypeAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_LongtermDebtTypeDomain" xlink:to="alks_TwentyTwentySixTermLoansMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_VariableRateAxis" order="10100.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateDomain_2" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateDomain" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_LondonInterbankOfferedRateLIBORMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_IncomeStatementLocationAxis" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" order="10210.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_InterestExpenseMember" order="10230.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentMaturityDate" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentDescriptionOfVariableRateBasis" order="10280.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" order="10300.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="alks_DebtInstrumentVariableRateBasisFloor" order="10320.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="alks_DebtInstrumentIncrementalCapacitySubjectToSatisfactionOfCertainConditions" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_ShortTermDebtRefinancedAmount" order="10390.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureShareBasedCompensationScheduleOfShareBasedCompensationExpenseDetails" xlink:href="alks-20220630.xsd#Role_DisclosureShareBasedCompensationScheduleOfShareBasedCompensationExpenseDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureShareBasedCompensationScheduleOfShareBasedCompensationExpenseDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:type="locator" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember" xlink:type="locator" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpensesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:type="locator" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_CostOfSalesMember" xlink:type="locator" xlink:label="us-gaap_CostOfSalesMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationDomain" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncomeStatementLocationAxis" xlink:type="locator" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:type="locator" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="us-gaap_IncomeStatementLocationAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_CostOfSalesMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_ResearchAndDevelopmentExpenseMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpensesMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" order="10160.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLossEarningsPerShareScheduleOfBasicLossEarningsPerOrdinaryShareDetails" xlink:href="alks-20220630.xsd#Role_DisclosureLossEarningsPerShareScheduleOfBasicLossEarningsPerOrdinaryShareDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLossEarningsPerShareScheduleOfBasicLossEarningsPerOrdinaryShareDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" xlink:type="locator" xlink:label="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_DilutiveSecuritiesAbstract" xlink:type="locator" xlink:label="us-gaap_DilutiveSecuritiesAbstract" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:type="locator" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_NetIncomeLoss" xlink:type="locator" xlink:label="us-gaap_NetIncomeLoss" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:type="locator" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain_2" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" order="10050.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" order="10080.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain_2" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" order="10130.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" order="10150.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_NetIncomeLoss" order="10180.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" order="10260.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_DilutiveSecuritiesAbstract" order="10340.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements" order="10500.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment" order="10660.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" order="10740.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLossEarningsPerShareScheduleOfAntiDilutiveOutstandingCommonShareEquivalentExcludedFromCalculationOfNetLossEarningsPerShareDetails" xlink:href="alks-20220630.xsd#Role_DisclosureLossEarningsPerShareScheduleOfAntiDilutiveOutstandingCommonShareEquivalentExcludedFromCalculationOfNetLossEarningsPerShareDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureLossEarningsPerShareScheduleOfAntiDilutiveOutstandingCommonShareEquivalentExcludedFromCalculationOfNetLossEarningsPerShareDetails">
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:type="locator" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_EmployeeStockOptionMember" xlink:type="locator" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:type="locator" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:type="locator" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" order="10110.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" order="10140.00" priority="2" use="optional" />
  </link:definitionLink>
  <link:roleRef roleURI="http://www.alkermes.com/20220630/taxonomy/role/DisclosureCommitmentsAndContingentLiabilitiesAdditionalInformationDetails" xlink:href="alks-20220630.xsd#Role_DisclosureCommitmentsAndContingentLiabilitiesAdditionalInformationDetails" xlink:type="simple" />
  <link:definitionLink xlink:type="extended" xlink:role="http://www.alkermes.com/20220630/taxonomy/role/DisclosureCommitmentsAndContingentLiabilitiesAdditionalInformationDetails">
    <link:loc xlink:href="alks-20220630.xsd#alks_MaximumPeriodBeforeFDACanApprovePatentRequest" xlink:type="locator" xlink:label="alks_MaximumPeriodBeforeFDACanApprovePatentRequest" />
    <link:loc xlink:href="alks-20220630.xsd#alks_NumberOfLicenseAgreementsPartiallyTerminated" xlink:type="locator" xlink:label="alks_NumberOfLicenseAgreementsPartiallyTerminated" />
    <link:loc xlink:href="https://xbrl.fasb.org/us-gaap/2022/elts/us-gaap-2022.xsd#us-gaap_LossContingencyAccrualProvision" xlink:type="locator" xlink:label="us-gaap_LossContingencyAccrualProvision" />
    <link:loc xlink:href="alks-20220630.xsd#alks_JanssenPharmaceuticaNVMember" xlink:type="locator" xlink:label="alks_JanssenPharmaceuticaNVMember" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:type="locator" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <link:loc xlink:href="https://xbrl.fasb.org/srt/2022/elts/srt-2022.xsd#srt_CounterpartyNameAxis" xlink:type="locator" xlink:label="srt_CounterpartyNameAxis" />
    <link:loc xlink:href="alks-20220630.xsd#alks_CommitmentsAndContingenciesTable" xlink:type="locator" xlink:label="alks_CommitmentsAndContingenciesTable" />
    <link:loc xlink:href="alks-20220630.xsd#alks_CommitmentsAndContingenciesLineItems" xlink:type="locator" xlink:label="alks_CommitmentsAndContingenciesLineItems" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="alks_CommitmentsAndContingenciesLineItems" xlink:to="alks_CommitmentsAndContingenciesTable" order="10010.00" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="alks_CommitmentsAndContingenciesTable" xlink:to="srt_CounterpartyNameAxis" order="10040.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" order="10070.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="alks_JanssenPharmaceuticaNVMember" order="10090.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="alks_CommitmentsAndContingenciesLineItems" xlink:to="us-gaap_LossContingencyAccrualProvision" order="10120.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="alks_CommitmentsAndContingenciesLineItems" xlink:to="alks_NumberOfLicenseAgreementsPartiallyTerminated" order="10170.00" priority="2" use="optional" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="alks_CommitmentsAndContingenciesLineItems" xlink:to="alks_MaximumPeriodBeforeFDACanApprovePatentRequest" order="10220.00" priority="2" use="optional" />
  </link:definitionLink>
</link:linkbase>
