ClinicalTrials.gov (v2 API)

Base URL

https://clinicaltrials.gov/api/v2/

Auth

No API key required. Fully public.

Key Endpoints

API version and data freshness

GET /version

Check dataTimestamp before time-sensitive retrievals to confirm the daily refresh has completed. ClinicalTrials.gov notes that data is generally refreshed Monday through Friday by 9 a.m. ET / 14:00 UTC.

ClinicalTrials.gov modernized its data ingest on August 26, 2025. For reproducible comparisons against older exports, note that some rich text markup fields and location/geopoint data may differ from the legacy pipeline.

Search studies

GET /studies

Key parameters: - query.cond — condition/disease (e.g. breast cancer) - query.intr — intervention/treatment (e.g. pembrolizumab) - query.term — general search terms - query.spons — sponsor - query.id — NCT ID - filter.overallStatus — pipe-delimited: RECRUITING|COMPLETED|ACTIVE_NOT_RECRUITING|... - filter.phase — PHASE1|PHASE2|PHASE3|PHASE4|NA - filter.geo — distance(lat,lon,dist) e.g. distance(38.89,-77.03,50mi) - fields — comma-separated field list to reduce payload - sort — e.g. LastUpdatePostDate:desc - pageSize — results per page (default 10, max 1000) - pageToken — cursor for next page (from nextPageToken in response) - countTotal=true — include total count

Example — recruiting Phase 3 breast cancer trials:

/studies?query.cond=breast+cancer&filter.overallStatus=RECRUITING&filter.phase=PHASE3&pageSize=5&countTotal=true

Response structure:

{
  "totalCount": 1234,
  "studies": [
    {
      "protocolSection": {
        "identificationModule": {"nctId": "NCT05123456", "briefTitle": "..."},
        "statusModule": {"overallStatus": "RECRUITING"},
        "designModule": {"phases": ["PHASE3"], "enrollmentInfo": {"count": 500}},
        "conditionsModule": {"conditions": ["Breast Cancer"]},
        "eligibilityModule": {"minimumAge": "18 Years", "sex": "ALL"}
      }
    }
  ],
  "nextPageToken": "CAYQAg"
}

Single study by NCT ID

GET /studies/{nctId}

Example: /studies/NCT05123456

Study count

GET /stats/size?query.cond={condition}&filter.overallStatus=RECRUITING

Field metadata

GET /studies/metadata

Pagination

Uses cursor-based pagination via pageToken (NOT numeric offsets). Include countTotal=true on first request to get total.

Rate Limits

No API key. Be reasonable — a few requests per second.

Bulk download

Prefer the v2 /studies API with pageToken pagination for programmatic retrieval. The former bulk URL https://clinicaltrials.gov/AllAPIJSON.zip returns 404 and must not be used.

For a full-registry XML dump, use:

https://clinicaltrials.gov/AllPublicXML.zip

That path redirects to https://clinicaltrials.gov/api/legacy/public-xml?format=zip and returns Content-Type: application/zip (ctg-public-xml.zip). Confirm the redirect still yields a zip before large downloads; CSV / pipe-delimited export options are documented under ClinicalTrials.gov Data API “Download” pages when XML is not appropriate.