ClinicalTrials.gov is a free public database run by the U.S. National Library of Medicine, part of the National Institutes of Health. To find ongoing or completed studies, go to clinicaltrials.gov, type a condition, drug, or supplement name into the search bar, then use the filters for location, status, and study type to narrow the list. Each result opens into a full study record with an identifier called an NCT number, which you can save or share with a clinician.
This guide walks through the search screen, explains what the status labels mean, and shows how to read a study record once you find one. It does not tell you whether any specific study applies to your situation — that judgment call belongs to you and a qualified clinician.
Before You Search: Know What You’re Looking For
A focused search saves time and avoids a wall of irrelevant results. Before you start, it helps to know:
- The condition or topic — the diagnosis, ingredient, or health question you want studies about.
- Whether you want ongoing or completed studies, they require different status filters, covered below.
- A rough location — useful only if you’re looking for a study you or someone else might join, not needed for general research.
- Why you’re searching — general background reading has a lower bar than deciding whether to enroll in a trial or bring a study to a doctor’s appointment.
Step-by-Step: Searching ClinicalTrials.gov
- Start with the search bar. Enter a condition, intervention, or keyword (for example, “vitamin D deficiency” or a drug name). ClinicalTrials.gov also accepts an NCT number directly if you already have one.
- Apply the status filter. This is the filter most people miss. Leaving it blank returns studies in every stage, including ones that have not started enrolling yet.
- Narrow by location, if relevant. If you are exploring whether to join a trial, filter by country, state, or distance from a ZIP code.
- Filter by study type and phase, if relevant. Interventional studies test a treatment; observational studies watch outcomes without assigning a treatment. Phase filters (Phase 1 through 4) apply to drug and biologic trials, not to every study.
- Open a result to view the full study record. This is where the real evaluation happens — see the next section.
Understanding Study Status Labels
Every study on ClinicalTrials.gov carries a status. Knowing what each one means prevents two common mistakes: assuming a study is finished when it isn’t, and assuming a “completed” study has posted results when it hasn’t.
- Not yet recruiting — the study is registered but has not started enrolling participants.
- Recruiting — the study is currently enrolling participants.
- Enrolling by invitation — participants are selected from a specific pre-identified group, not the general public.
- Active, not recruiting — the study is ongoing (participants are still being followed or treated), but no one new is being enrolled.
- Completed — the study has ended for all participants. Results may or may not be posted yet.
- Suspended — the study has been paused, sometimes temporarily, before completion.
- Terminated — the study stopped early, before its planned end.
- Withdrawn — the study stopped before enrolling any participants.
- Unknown status — the last known status has not been confirmed or updated within the expected timeframe.
A “Completed” status is not the same as “results available.” Some completed studies never post results on the site, and others take time to appear after the study ends. Check the record’s results section directly rather than assuming.
How to Read a Study Record
Once you open a study, look for these sections. They exist on nearly every record, though the amount of detail varies:
- NCT number. The permanent ID (format: NCT followed by eight digits). Use this number if you want to reference the study precisely with a clinician or search for it elsewhere, including PubMed.
- Status and dates. Recruitment status, start date, and primary completion or study completion date.
- Study design. Whether it’s interventional or observational, the phase (if applicable), and how participants were grouped — for example, randomized versus non-randomized, or blinded versus open-label.
- Eligibility criteria. Age range, sex, and the inclusion/exclusion requirements. This is a public summary, not the full clinical protocol, and it does not tell you whether you personally would qualify.
- Interventions and outcome measures. What was tested (a drug, supplement, device, or procedure) and what was measured — the primary outcome and any secondary outcomes.
- Sponsor and collaborators. Who funded and ran the study. This matters for judging potential conflicts of interest.
- Locations and contacts. Where the study is or was conducted, and contact information if it’s still recruiting.
- Results (when posted). Participant flow, baseline characteristics, outcome data, and adverse events. Not every study has this section filled in, even after completion.
For a deeper walkthrough of how to weigh study design, sample size, and statistical versus practical significance once you’ve opened a record, see How to Read a Clinical Study and Understanding Study Design Types.
Finding Published Results: ClinicalTrials.gov and PubMed Together
A study record on ClinicalTrials.gov may link to a published paper, but not every study does, and not every published paper is linked back to its registration. PubMed, maintained by the National Library of Medicine’s National Center for Biotechnology Information, indexes more than 40 million citations from biomedical journals. If a ClinicalTrials.gov record doesn’t show a linked publication, you can search pubmed.ncbi.nlm.nih.gov using the study’s NCT number as a search term — many journal articles list it, since major journals now require trial registration for publication.
Cross-checking both sites matters because a registration record and a published paper can tell different parts of the same story: the registration shows what was planned and, if posted, the raw outcome data; the published paper adds the authors’ interpretation, discussion of limitations, and context from other research.
Quick Decision Path
- Want to see what’s currently being studied? Search by condition or ingredient, filter status to “Recruiting” or “Not yet recruiting.”
- Want to see what’s already been studied? Filter status to “Completed,” then check whether a results section or linked publication is present.
- Have a specific study in mind? Search its NCT number directly, or search that same number on PubMed to find any published paper.
- Considering joining a trial? Filter by location and recruiting status, then review eligibility criteria and contact information — and talk to a qualified clinician before applying.
Evidence Limits to Keep in Mind
- Registration is not proof of a finding. A study appearing on ClinicalTrials.gov means it was registered, not that it produced a meaningful or reliable result.
- Not all studies post results. A completed study without a results section may still be in progress toward publication, or its results may never be posted on the site.
- A single study rarely settles a question. Look for whether other studies have found similar results before treating any one study as conclusive. See Evaluating Evidence Quality for a framework on weighing multiple studies.
- Small or early-phase studies carry more uncertainty. Phase 1 trials mainly test safety in small groups, not effectiveness.
- Funding source is public but requires judgment. A sponsor’s identity doesn’t automatically invalidate a study, but it’s worth knowing — see Research Funding and Conflicts of Interest.
Who Should Use Extra Caution
Anyone considering enrolling in a trial — including pregnant people, children (through a parent or guardian), older adults, and people managing an existing condition or taking other medications — should review eligibility criteria carefully and discuss participation with a qualified clinician before contacting a study team. Eligibility criteria listed on ClinicalTrials.gov are a public summary, not a final determination, and only the study team can confirm whether someone qualifies.
FAQ
Is ClinicalTrials.gov free to use?
Yes. It’s a public database maintained by the National Library of Medicine, and no account or payment is required to search or view study records.
What does an NCT number mean?
It’s the permanent identifier assigned to a study when it’s registered, formatted as “NCT” followed by eight digits. It stays the same even if the study’s title or sponsor changes later.
Why can’t I find results for a study marked “Completed”?
Not every completed study has posted results on the site. Some are still working toward publication, and posting a full results section is not required in every case.
Can I use ClinicalTrials.gov to decide whether to take a supplement or medication?
You can use it to see what research exists, but the site itself does not make recommendations, and neither should a single study. Bring what you find to a qualified clinician who knows your health history before making any decision.
This article is for educational purposes only and does not provide medical advice, diagnosis, or treatment recommendations. Always talk with a qualified healthcare provider before starting, stopping, or changing any medication, supplement, or treatment, or before deciding whether to participate in a clinical trial.