ClinicalTrials.gov API
Provides programmatic access to the NIH ClinicalTrials.gov database of over 450,000 clinical studies worldwide, enabling search, retrieval, and analysis of trial metadata, eligibility criteria, results, and status.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
HTTPS enforced. No auth means no scope granularity possible. Public read-only data so low auth strength is appropriate. pytrials library is lightly maintained with infrequent updates.
⚡ Reliability
Best When
An agent needs to search or monitor clinical trial data for research, patient matching, or regulatory analysis.
Avoid When
You need real-time enrollment data, patient-level outcomes, or trials from regions that don't register with ClinicalTrials.gov.
Use Cases
- • Finding open clinical trials for patients with specific conditions
- • Regulatory research and competitive intelligence for pharma/biotech
- • Evidence synthesis and systematic review automation
- • Tracking trial status changes and result postings
- • Eligibility screening by matching patient criteria to trial requirements
Not For
- • Real-time patient enrollment or trial participation management
- • Accessing individual patient-level data (only aggregate results available)
- • Non-US-registered trials that don't report to ClinicalTrials.gov
Interface
Authentication
Fully open public API with no authentication required. No API key, no registration. Rate limiting is enforced by IP but not formally documented.
Pricing
Completely free public API operated by the US National Library of Medicine. No rate limit tiers or paid plans.
Agent Metadata
Known Gotchas
- ⚠ v1 API was deprecated in favor of v2 (2023); some third-party docs still reference the old endpoint structure
- ⚠ Query syntax uses a custom filter format (e.g., AREA[...]) that is non-obvious and poorly documented for agents
- ⚠ Large result sets can be slow; pageSize max is 1000 but deep pagination degrades performance
- ⚠ Trial status vocabulary is extensive and inconsistent — 'Recruiting', 'Not yet recruiting', etc. must be matched exactly
- ⚠ Date fields use inconsistent formats across record types
Alternatives
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for ClinicalTrials.gov API.
Scores are editorial opinions as of 2026-03-06.