Clinical trials API with the full change history.

The Posolix clinical trials API gives you public US trial registry data through one REST API. Search trials by condition, sponsor, phase or status, then pull every change we've recorded for a trial, from registration to results.

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7-day free trial, then API plans from $149 a month. See pricing.

# Recruiting phase 3 lung cancer trials
GET /v1/trials?condition=lung+cancer
  &phase=PHASE3&status=RECRUITING

{
"data": [
  {
    "nct_id": "NCT0XXXXXXX",
    "title": "First-line combination in advanced disease",
    "phase": "PHASE3",
    "overall_status": "RECRUITING",
    "sponsor": "Sample Bio",
    "enrollment": 780,
    "last_changed_at": "2026-09-16T08:40:00Z"
  }
],
"next_cursor": "eyJpZCI6IjE4MjQ..."
}  // illustrative, fields may change

Clinical trial data endpoints.

Three endpoints cover search, a single trial and its history. Every response uses the same normalized fields, so you don't have to handle the registry's nested study format yourself.

GET/v1/trials
Search trials by condition, sponsor, phase, status and last-change date. Cursor pagination, sorted by latest change.
GET/v1/trials/:nct_id
One trial's current record: title, conditions, interventions, sponsor, phase, status, enrollment, key dates and sites.
GET/v1/trials/:nct_id/history
Every version of the trial we've stored, with the fields that changed between each version.

See how a trial changed, not just where it is now.

The public registry returns only the current version of a study. When a sponsor moves a completion date, cuts enrollment or pauses recruiting, the old values are hard to get back.

Posolix fetches every trial on a schedule, stores a new version whenever something changes and records what changed. The history endpoint returns that timeline, so you can see a trial slipping or speeding up without keeping your own copy of the registry.

Want each change as it happens? The same events arrive as clinical trial webhooks, or as email alerts if you don't write code.

GET /v1/trials/NCT0XXXXXXX/history

{
"nct_id": "NCT0XXXXXXX",
"versions": [
  {
    "detected_at": "2026-09-16T08:40:00Z",
    "event": "trial.completion_date_changed",
    "changes": {
      "primary_completion_date": {
        "from": "2027-03", "to": "2027-11"
      }
    }
  },
  {
    "detected_at": "2026-06-02T11:15:00Z",
    "event": "trial.enrollment_changed",
    "changes": {
      "enrollment": { "from": 620, "to": 780 }
    }
  }
]
}  // illustrative

Trial changes we track.

Each change is stored as a typed event you can filter on in the API, or subscribe to by webhook.

trial.registeredA new NCT ID appears in the registry.

trial.status_changedRecruitment status changes, for example Recruiting to Active, not recruiting.

trial.phase_changedThe trial's phase changes.

trial.enrollment_changedEnrollment count or type (estimated or actual) changes.

trial.completion_date_changedThe primary or study completion date moves.

trial.results_postedA results section appears for the first time.

Who uses a clinical trial data API.

Health-tech developersPower trial search or patient matching in your product without parsing the raw registry.

Biotech and pharma teamsTrack competitor trials by condition or sponsor and see every status and timeline change.

Investors and analystsBacktest how trial events line up with catalysts, using the full event history.

ResearchersStudy how registrations change over time, such as enrollment revisions and delayed results.

Questions.

Is this an official government API?

No. Posolix builds on public US government trial data, stores every version of every trial and adds change history, typed events and webhooks on top. We are not affiliated with or endorsed by any government agency.

Which trials are covered?

Every study in the public US trial registry. History starts from the first version we fetch, so changes made before we started tracking a trial only show as its starting state.

Can I get changes pushed to me instead of polling?

Yes. The same trial events are available as signed webhooks. Subscribe with a filter and we POST each matching change to your endpoint.

How much does the clinical trials API cost?

API access is on the API plan at $149 a month (100,000 requests, 5 webhook endpoints) or the Team plan at $499 a month. Yearly billing gets you a month free, and every account starts with a 7-day free trial. See pricing.

Get a clinical trials API key.

Create your account and get an API key right away. Your first 7 days are free, no card needed.

Try for free