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Finding a Clinical Trial on ClinicalTrials.gov
A practical guide to searching ClinicalTrials.gov — how to filter by condition, drug, location, and phase, what the NCT number means, and how to contact a study site.
Patients, caregivers, and researchers who want to find ongoing studies enrolling participants, understand search results, and take the next step toward contacting a trial site.
ClinicalTrials.gov is the federal government’s registry of clinical research studies. Every trial registered there is assigned a unique NCT number, and the record includes who is running the study, what they are testing, who is eligible, and — critically — how to reach someone at the study site. Knowing how to search the database effectively can save hours of dead-end calls and help you find studies that match your situation.
What ClinicalTrials.gov is and who maintains it
The database is operated by the U.S. National Library of Medicine, a component of the National Institutes of Health. It was launched in 2000 and now contains records for hundreds of thousands of studies — conducted in every U.S. state and in more than 200 countries.
Sponsors — pharmaceutical companies, academic medical centers, NIH institutes, and others — are required by federal law to register most clinical trials of drugs, biologics, and devices regulated by the FDA. Federally funded trials have their own registration requirements. The result is a single searchable index of nearly all significant research studies seeking human participants.
How to search: a step-by-step approach
Step 1: Start with your condition or treatment
On the ClinicalTrials.gov home page, the primary search box accepts condition names, disease names, drug names, or free-text keywords. Start broad — search “type 2 diabetes” rather than a lengthy clinical description. You can narrow from there.
Step 2: Apply filters
The search results page offers filters on the left side. The most useful for a patient searching for a study to join are:
| Filter | What it does |
|---|---|
| Recruitment status | Limits results to trials actively enrolling participants (“Recruiting”) |
| Age | Filters to studies that include your age group |
| Study phase | Phase 1–4, or N/A for non-drug studies; Phase 2–3 trials are often the best fit for patients seeking treatment access |
| Location | Enter a city, state, or ZIP code and a radius to find nearby sites |
| Sponsor/collaborator | Filter by the funding organization (useful if you want NIH-sponsored vs. industry-sponsored studies) |
Applying “Recruiting” and your location in the same search dramatically reduces results to only studies you could realistically join.
Step 3: Read the trial record
Clicking a study title opens the full record. The key sections are:
- Eligibility — lists inclusion and exclusion criteria in detail
- Description — plain-language and technical descriptions of what the study is testing
- Contacts and Locations — shows all registered study sites and the contact information for each
- More Information — often includes links to the sponsor’s website or a dedicated study recruitment page
Step 4: Check the NCT number
Every study record includes an NCT number — a unique identifier formatted as NCT followed by eight digits. Write this down. When you call or email a trial site, citing the NCT number ensures both you and the coordinator are looking at the same study, especially if the site runs multiple trials.
Step 5: Contact the site directly
The Contacts and Locations section lists the name and contact information for each study site. Most list a study coordinator’s phone number and email. Call or email that contact — not the sponsor’s general phone number — to ask about current enrollment status and whether you might qualify based on your medical history.
Understanding trial phases
Trials are classified by phase, which signals what question the study is trying to answer:
- Phase 1: Is it safe? Small groups (often 20–80 participants), often healthy volunteers or patients with no remaining standard options; primarily tests dosing and side effects.
- Phase 2: Does it work, and what dose is right? Larger groups (often 100–300 participants); begins to assess efficacy.
- Phase 3: Is it better than the current standard? Large groups (often hundreds to thousands); the pivotal trial that precedes FDA approval. Patients seeking access to a promising treatment are most commonly enrolled at Phase 3.
- Phase 4: Post-market surveillance. Conducted after a drug is already approved; tracks long-term safety and effectiveness in a broad population.
If you are looking for access to an experimental treatment that has not yet been approved, Phase 2 and Phase 3 trials are typically where you would look.
Reading eligibility criteria carefully
Eligibility criteria are the gatekeeping rules of a trial. They are divided into:
- Inclusion criteria — characteristics you must have to qualify (e.g., a specific diagnosis, an age range, a disease stage, a particular lab value)
- Exclusion criteria — characteristics that disqualify you (e.g., prior use of a specific medication, a co-occurring condition, pregnancy, or current participation in another trial)
Do not self-disqualify before calling. Exclusion criteria are often more specific than they appear in plain language, and a coordinator can clarify whether your particular situation triggers a given criterion. At the same time, do not enroll in a trial for which you do not meet the criteria — it harms both you and the validity of the research.
Documents and terms you’ll see
When reviewing a ClinicalTrials.gov record, you will encounter these terms:
- NCT number — the trial’s unique identifier; use it when contacting the site or referencing the study with your doctor
- Trial phase — tells you where the trial is in the research process and what its primary goal is
- Principal investigator — the lead researcher at a given site; listed in the Contacts and Locations section
- Eligibility criteria — the specific requirements to participate; read both inclusion and exclusion criteria before contacting a site
What to say when you contact a trial site
When you reach the study coordinator, have this information ready:
- The NCT number of the study you are calling about
- Your diagnosis and current stage or severity, if relevant
- A brief list of current medications (especially anything flagged as an exclusion criterion in the record)
- Your location and whether you can travel to the study site
- Whether your insurance has been informed and whether it covers routine trial costs
The coordinator’s job includes screening potential participants, so they will ask you similar questions. Being prepared shortens the call and increases the chances of getting a clear answer about whether you are a likely candidate.
If you do not find a match
Not every condition has an active recruiting trial, and not every trial accepts out-of-area participants. If your initial search returns nothing suitable:
- Broaden to nearby states (expand the location radius)
- Remove the Phase filter to see all phases, including early studies
- Check condition-specific advocacy organizations — many maintain their own trial registries and can flag studies not prominently appearing in ClinicalTrials.gov searches
- Ask your treating physician to search — they may have relationships with investigators running trials that are not yet heavily publicized
For background on what happens once you enroll — including who pays for what — see the who pays in a clinical trial page, and the broader clinical trials and how research studies work guide for an overview of the research process.
Key terms
| Term | Plain meaning | Glossary |
|---|---|---|
| NCT number | A unique identifier assigned to every registered clinical trial on ClinicalTrials.gov, formatted as NCT followed by eight digits (e.g., NCT01234567) | → |
| Trial phase | A stage in the clinical trial process — Phase 1 tests safety in a small group, Phase 2 tests efficacy and dosing, Phase 3 compares to standard treatment in a large group, Phase 4 monitors approved treatments after market release | → |
| Eligibility criteria | The specific medical, demographic, and logistical requirements a person must meet — or must not have — to participate in a given study | → |
| Principal investigator | The lead researcher responsible for conducting the clinical trial at a given site; listed in the trial record and often the contact point for enrollment questions | → |
Common questions
- What is ClinicalTrials.gov?
- ClinicalTrials.gov is a publicly accessible database maintained by the U.S. National Library of Medicine. It contains records for tens of thousands of clinical studies — both ongoing and completed — conducted in the United States and in many other countries.
- Who is required to register a trial on ClinicalTrials.gov?
- Under the FDA Amendments Act of 2007, most clinical trials of drugs, biologics, and devices subject to FDA regulation must be registered on ClinicalTrials.gov. Many federally funded trials are also required to register and report results.
- How do I search for trials by my condition?
- On the ClinicalTrials.gov home page, enter your condition or disease name in the search box. You can then narrow results by location (city, state, or ZIP code), recruitment status (recruiting, not yet recruiting, active not recruiting), age, and study phase using the left-side filters.
- What does 'Recruiting' mean in a trial status?
- Recruiting means the trial is actively seeking participants who meet the eligibility criteria. Not yet recruiting means the trial has been registered but has not yet started enrolling. Active, not recruiting means enrollment is closed but the study is still ongoing.
- How do I contact a trial site?
- Each trial record on ClinicalTrials.gov includes a Contacts and Locations section. This lists the study sites, the names of contact people at each site, and phone numbers or email addresses. Contact the site directly — the national sponsor's phone number listed on the record may route you to a call center that can also direct you.
- What are inclusion and exclusion criteria?
- Eligibility criteria are split into inclusion criteria (requirements you must meet to participate, such as a specific diagnosis or age range) and exclusion criteria (conditions or characteristics that disqualify you, such as current use of a particular medication). Read both carefully before contacting a site.
- Can I participate in a trial if I live far from the research site?
- Distance is a common barrier. Some trials have multiple sites across the country or the world — check the Locations tab to see all registered sites. Increasingly, some trials include virtual or decentralized components that reduce required in-person visits.
- Is information in ClinicalTrials.gov always up to date?
- Sponsors are required to update trial records regularly, but delays do occur. If a record shows that a trial is recruiting but you cannot reach the contact, the trial may have quietly closed or paused enrollment. Always call or email the site directly to confirm current status.
Sources
Last reviewed: September 2026