This code system http://hl7.org/fhir/research-study-reason-stopped defines the following codes:

Code Display Definition
accrual-goal-met Accrual Goal Met The study prematurely ended because the accrual goal was met.
closed-due-to-toxicity Closed due to toxicity The study prematurely ended due to toxicity.
closed-due-to-lack-of-study-progress Closed due to lack of study progress The study prematurely ended due to lack of study progress.
temporarily-closed-per-study-design Temporarily closed per study design The study prematurely ended temporarily per study design.
<status value="active"/> <experimental value="false"/> <date value="2022-05-15T16:55:11.085+11:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="Codes for why the study ended prematurely."/> <jurisdiction> <coding> <system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/> <code value="001"/> <display value="World"/> </coding> </jurisdiction> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/research-study-reason-stopped"/> <content value="complete"/> <concept> <code value="accrual-goal-met"/> <display value="Accrual Goal Met"/> <definition value="The study prematurely ended because the accrual goal was met."/> </concept> <concept> <code value="closed-due-to-toxicity"/> <display value="Closed due to toxicity"/> <definition value="The study prematurely ended due to toxicity."/> </concept> <concept> <code value="closed-due-to-lack-of-study-progress"/> <display value="Closed due to lack of study progress"/> <definition value="The study prematurely ended due to lack of study progress."/> </concept> <concept> <code value="temporarily-closed-per-study-design"/> <display value="Temporarily closed per study design"/> <definition value="The study prematurely ended temporarily per study design."/> </concept> </CodeSystem>