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

CodeDisplay
active-comparator Active Comparator
placebo-comparator Placebo Comparator
sham-comparator Sham Comparator
no-intervention No Intervention
experimental Experimental
other-arm-type Other Arm Type
<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 the main intent of the study."/><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-arm-type"/><content value="complete"/><concept><code value="active-comparator"/><display value="Active Comparator"/></concept><concept><code value="placebo-comparator"/><display value="Placebo Comparator"/></concept><concept><code value="sham-comparator"/><display value="Sham Comparator"/></concept><concept><code value="no-intervention"/><display value="No Intervention"/></concept><concept><code value="experimental"/><display value="Experimental"/></concept><concept><code value="other-arm-type"/><display value="Other Arm Type"/></concept></CodeSystem>