ClinicalTrials.gov

Key facts

Operated by

National Library of Medicine (NLM), National Institutes of Health

Launched

2000, following a mandate in FDAMA 1997

Reporting rules

FDAAA Section 801 and 42 CFR Part 11; NIH clinical trial policy

Record identifier

NCT number: the letters NCT followed by 8 digits

Access

Public website and a free REST API (version 2) returning JSON

What is ClinicalTrials.gov?

ClinicalTrials.gov is a registry of privately and publicly funded clinical studies conducted around the world. Congress required a public trials database in the Food and Drug Administration Modernization Act of 1997 (FDAMA), and the National Library of Medicine (NLM) launched the site in 2000.

The Food and Drug Administration Amendments Act of 2007 (FDAAA) expanded the mandate. Its Section 801, implemented by the final rule at 42 CFR Part 11, requires responsible parties to register applicable clinical trials and, for many of them, submit summary results. A separate NIH policy requires registration and results reporting for NIH-funded clinical trials.

Sponsors and investigators enter records through the Protocol Registration and Results System (PRS). NLM staff review submissions for apparent errors and inconsistencies, but a listing does not mean the study has been evaluated or endorsed by the federal government.

How ClinicalTrials.gov records are structured

Each study record carries a fixed set of data elements, including:

• Identifiers: the NCT number, the sponsor protocol ID and other secondary IDs.
• Study type and design: interventional, observational or expanded access, plus phase, allocation and masking.
• Conditions, interventions and outcome measures, including primary and secondary endpoints.
• Lead sponsor and collaborators, eligibility criteria, enrollment, and key dates such as start and primary completion.
• Overall recruitment status and a list of locations, each with its own recruitment status.
• Results, when posted: participant flow, baseline characteristics, outcome measures and adverse events.

Why ClinicalTrials.gov matters

It is the main public source for tracking who is testing what, where and when, and it is used well beyond the United States.

• Pipeline and competitive intelligence: filter by condition, intervention, phase and sponsor.
• Site and investigator selection: location lists show which facilities have run trials in a disease area.
• Patient recruitment: recruiting status and eligibility criteria show open studies by geography.
• Transparency research: registration and results fields show whether trials report on time.

Limitations of ClinicalTrials.gov data

Data quality depends on the people who submit it. Condition, intervention, sponsor and facility names are largely free text, so the same drug or hospital can appear under many spellings; the site adds derived Medical Subject Headings (MeSH) terms to help group conditions and interventions.

Status and dates are self-reported and often go stale. Studies that were still listed as recruiting or active, have passed their completion date and have not been verified in two years are shown with an unknown status. Enrollment can be anticipated or actual, so counts need checking before they drive decisions.