The following table shows usefule REST and API Services related to clinical study evaluations. Please let me know if you are aware of other services to include them here.

ServiceProviderDescription / Link

OpenFDA is an Elasticsearch-based API that serves public FDA data about nouns like drugs, devices, and foods.

ClinicalTrials.govNIH - U.S. National Library of Medicine

Access ClinicalTrials.gov study records data

UML REST ServicesNIH - U.S. National Library of MedicineUMLS REST API Home Page (Unified Medical Language System)
UCUM RESTful Web ServicesNIH - U.S. National Library of MedicineUCUM validation and unit conversions service, including "Conventional" to "SI" unit conversions and vice versa (Unified Code for Units of Measure)
Cancer Clinical Trials API (Beta)NIH - U.S. National Library of Medicinehttps://www.cancer.gov/syndication/api
CDISC API (requires account)CDISChttps://www.cdisc.org/cdisc-library/api-documentation
CDISC-CT servicesXML4Pharma CDISC Controlled Terminology services
CDISC Domains / Standards Versions Web Services XML4Pharma CDISC SDTM/SEND domain information services
CDISC SDS/SDTM Variable Web Services XML4Pharma CDISC SDTM/SEND variable information services
LOINC to CDISC Mapping Web Services (LB,MB,VS) XML4PharmaRESTful web services implementing LOINC to CDISC mappings