18Check `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.

20ClinicalTrials.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.

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.

Raw lines 13 to 21

22### Search studies

23```

24GET /studies

25```

27Key parameters:

28- `query.cond` — condition/disease (e.g. `breast cancer`)

29- `query.intr` — intervention/treatment (e.g. `pembrolizumab`)

30- `query.term` — general search terms

31- `query.spons` — sponsor

32- `query.id` — NCT ID

33- `filter.overallStatus` — pipe-delimited: `RECRUITING|COMPLETED|ACTIVE_NOT_RECRUITING|...`

34- `filter.advanced` — Essie expression, e.g. `AREA[Phase]PHASE3`; there is no `filter.phase` parameter

35- `filter.geo` — `distance(lat,lon,dist)` e.g. `distance(38.89,-77.03,50mi)`

36- `fields` — comma-separated field list to reduce payload

37- `sort` — e.g. `LastUpdatePostDate:desc`

38- `pageSize` — results per page (default 10, max 1000)

39- `pageToken` — cursor for next page (from `nextPageToken` in response)

40- `countTotal=true` — include total count

42Example — recruiting Phase 3 breast cancer trials:

43```

44/studies?query.cond=breast+cancer&filter.overallStatus=RECRUITING&filter.advanced=AREA%5BPhase%5DPHASE3&pageSize=5&countTotal=true

45```

47Response structure:

48```json

49{

50 "totalCount": 1234,

51 "studies": [

52 {

53 "protocolSection": {

54 "identificationModule": {"nctId": "NCT05123456", "briefTitle": "..."},

55 "statusModule": {"overallStatus": "RECRUITING"},

56 "designModule": {"phases": ["PHASE3"], "enrollmentInfo": {"count": 500}},

57 "conditionsModule": {"conditions": ["Breast Cancer"]},

58 "eligibilityModule": {"minimumAge": "18 Years", "sex": "ALL"}

59 }

60 }

61 ],

62 "nextPageToken": "CAYQAg"

63}

64```

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.advanced — Essie expression, e.g. AREA[Phase]PHASE3; there is no filter.phase parameter
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.advanced=AREA%5BPhase%5DPHASE3&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"
}

Raw lines 22 to 65

66### Single study by NCT ID

67```

68GET /studies/{nctId}

69```

70Example: `/studies/NCT05123456`

Single study by NCT ID

GET /studies/{nctId}

Example: /studies/NCT05123456

Raw lines 66 to 71

72### Study count

73```

74GET /studies?query.cond={condition}&filter.overallStatus=RECRUITING&pageSize=1&countTotal=true

75```

77Read `totalCount` from the first response. `/stats/size` accepts no search parameters and reports registry-wide statistics, not a filtered count.

Study count

GET /studies?query.cond={condition}&filter.overallStatus=RECRUITING&pageSize=1&countTotal=true

Read totalCount from the first response. /stats/size accepts no search parameters and reports registry-wide statistics, not a filtered count.

Raw lines 72 to 78

79### Field metadata

80```

81GET /studies/metadata

82```

Field metadata

GET /studies/metadata

Raw lines 79 to 83

84## Pagination

85Uses cursor-based pagination via `pageToken` (NOT numeric offsets). Include `countTotal=true` on first request to get total.

Pagination

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

Raw lines 84 to 86

87## Rate Limits

88No API key. Be reasonable — a few requests per second.

Rate Limits

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

Raw lines 87 to 89

90## Bulk download

92Prefer the v2 `/studies` API with `pageToken` pagination for programmatic

93retrieval. The former bulk URL `https://clinicaltrials.gov/AllAPIJSON.zip`

94returns **404** and must not be used.

96For a full-registry **XML** dump, use:

98```

99https://clinicaltrials.gov/AllPublicXML.zip

100```

101

102That path redirects to `https://clinicaltrials.gov/api/legacy/public-xml?format=zip`

103and returns `Content-Type: application/zip` (`ctg-public-xml.zip`). Confirm the

104redirect still yields a zip before large downloads; CSV / pipe-delimited export

105options are documented under ClinicalTrials.gov Data API “Download” pages when

106XML is not appropriate.

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.

Raw lines 90 to 106