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<!--Generated by DFIN XBRL Instance Document - http://www.dfinsolutions.com/ - Version R3.0 - on 17-March-2023 [04:51:20] {PM}-->
<linkbase xmlns="http://www.xbrl.org/2003/linkbase" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">


  <roleRef xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#PvpAdjustmentsOnly" roleURI="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly"/>




  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>


  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>


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  <arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/notAll" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#notAll"/>


  <definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/ecd/role/PvpAdjustmentsOnly">


    <loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/ecd/2022q4/ecd-2022q4.xsd#ecd_AllAdjToCompMember" xlink:label="AllAdjToCompMember"/>


    <loc xlink:type="locator" xlink:href="lnth-20221231.xsd#lnth_SctValueOfStockAndOptionAwardsMember" xlink:label="SctValueOfStockAndOptionAwardsMember"/>


    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="SctValueOfStockAndOptionAwardsMember" order="100"/>


    <loc xlink:type="locator" xlink:href="lnth-20221231.xsd#lnth_FairValueAtYearendOfAwardsGrantedDuringTheCoveredFiscalYearThatAreOutstandingAndUnvestedAtYearendMember" xlink:label="FairValueAtYearendOfAwardsGrantedDuringTheCoveredFiscalYearThatAreOutstandingAndUnvestedAtYearendMember"/>


    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="FairValueAtYearendOfAwardsGrantedDuringTheCoveredFiscalYearThatAreOutstandingAndUnvestedAtYearendMember" order="101"/>


    <loc xlink:type="locator" xlink:href="lnth-20221231.xsd#lnth_YearOverYearChangeInFairValueOfAwardsGrantedInAnyPriorFiscalYearThatAreOutstandingAndUnvestedAtYearEndMember" xlink:label="YearOverYearChangeInFairValueOfAwardsGrantedInAnyPriorFiscalYearThatAreOutstandingAndUnvestedAtYearEndMember"/>


    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="YearOverYearChangeInFairValueOfAwardsGrantedInAnyPriorFiscalYearThatAreOutstandingAndUnvestedAtYearEndMember" order="102"/>


    <loc xlink:type="locator" xlink:href="lnth-20221231.xsd#lnth_ChangeAsOfTheVestingDateFromTheEndOfThePriorFiscalYearInFairValueOfAwardsGrantedInAnyPriorFiscalYearForWhichVestingConditionsWereSatisfiedDuringSuchYearMember" xlink:label="ChangeAsOfTheVestingDateFromTheEndOfThePriorFiscalYearInFairValueOfAwardsGrantedInAnyPriorFiscalYearForWhichVestingConditionsWereSatisfiedDuringSuchYearMember"/>


    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="ChangeAsOfTheVestingDateFromTheEndOfThePriorFiscalYearInFairValueOfAwardsGrantedInAnyPriorFiscalYearForWhichVestingConditionsWereSatisfiedDuringSuchYearMember" order="103"/>


    <loc xlink:type="locator" xlink:href="lnth-20221231.xsd#lnth_FairValueAtEndOfPriorYearOfAwardsGrantedInAnyPriorFiscalYearThatFailToMeetTheApplicableVestingConditionsDuringSuchYearMember" xlink:label="FairValueAtEndOfPriorYearOfAwardsGrantedInAnyPriorFiscalYearThatFailToMeetTheApplicableVestingConditionsDuringSuchYearMember"/>


    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllAdjToCompMember" xlink:to="FairValueAtEndOfPriorYearOfAwardsGrantedInAnyPriorFiscalYearThatFailToMeetTheApplicableVestingConditionsDuringSuchYearMember" order="104"/>


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