Signing up for a clinical trial starts with finding a study that matches your health profile, then passing a screening process to confirm you’re eligible. The whole process, from first search to enrollment, typically takes a few weeks. Most people begin at ClinicalTrials.gov, the largest public database of studies worldwide, but there are several other paths depending on your condition and location.
Finding Trials That Match Your Situation
ClinicalTrials.gov is the most comprehensive starting point. From the home page, you can search using three basic filters: your condition or disease (such as “type 2 diabetes” or “migraine”), a specific treatment you’re interested in (like a drug name or “physical therapy”), and your location. You can search by city, state, or country to find studies near you.
By default, the database shows all studies, including ones that finished years ago. To see only studies actively looking for participants, change the Study Status filter to “Recruiting and not yet recruiting.” This one adjustment dramatically narrows your results to trials you can actually join.
For more precise results, open the “More Filters” menu. You can filter by age group, trial phase, sex, and whether results have been posted. If you’re 70 and searching for a heart disease trial, for example, filtering by the “Older Adult (65+)” age group saves you from clicking through dozens of listings that cap enrollment at age 64.
Beyond ClinicalTrials.gov, the World Health Organization runs the International Clinical Trials Registry Platform at trialsearch.who.int, which pulls data from registries across multiple countries. Disease-specific organizations also offer trial-matching services. Many cancer centers and advocacy groups maintain their own searchable databases or will match you to a trial based on your diagnosis and treatment history.
Understanding Trial Phases
Each listing on ClinicalTrials.gov identifies the trial’s phase, which tells you a lot about what participation would look like. Phase I trials enroll small groups of 20 to 80 people and focus primarily on whether a treatment is safe and what side effects it causes. These carry the most uncertainty because the treatment hasn’t been tested widely in humans.
Phase II trials expand to 100 to 300 participants and begin measuring whether the treatment actually works, while continuing to track safety. Phase III trials are the largest, enrolling 1,000 to 3,000 people to confirm effectiveness, compare the new treatment against existing options, and build the evidence needed for regulatory approval. Phase IV trials happen after a drug is already approved and available to the public, tracking long-term safety and optimal use in real-world conditions.
For most people searching for a new treatment option, Phase II and Phase III trials offer the best balance of potential benefit and existing safety data. Phase I trials are more common for people with serious conditions who have exhausted standard treatments.
What Eligibility Criteria Look Like
Every trial listing includes two sets of requirements: inclusion criteria (what you need to have) and exclusion criteria (what disqualifies you). Inclusion criteria typically specify a particular diagnosis, disease stage, or biological marker. A cancer trial might require a specific genetic mutation. A diabetes trial might require a certain range of blood sugar levels.
Exclusion criteria tend to be broader. Chronic conditions other than the one being studied are a common reason for exclusion, because additional medications can interact with the experimental treatment or complicate the results. In one FDA analysis, over 60% of drug trials excluded people based on liver function tests, and 58% excluded based on kidney function. Roughly 27% of trials for diseases common in older adults set arbitrary upper age limits. Pregnant or lactating women have historically been excluded from most trials as well.
If you have multiple health conditions or take several medications, you may need to search through more listings before finding one that fits. Don’t assume you’re ineligible just because of your age or a secondary condition. Criteria vary widely between studies, and the FDA has been pushing sponsors to broaden their enrollment. Since 2022, federal law requires sponsors of late-stage drug and device trials to submit Diversity Action Plans with enrollment goals broken down by race, ethnicity, sex, and age.
How to Actually Enroll
Once you find a trial that fits, the listing will include contact information for the study coordinator or a link to express interest online. Your first interaction is usually a phone call or questionnaire where the coordinator asks about your medical history, current medications, and general health. This is a preliminary check against the eligibility criteria.
If you pass that initial screen, you’ll be invited for an in-person screening visit. This often includes blood work, imaging, or other tests to verify you meet the study’s medical requirements. Some trials have a single screening visit; others require several over a couple of weeks. Not everyone who screens will qualify. The research team will let you know whether you’ve been accepted.
Before any study procedures begin, you go through informed consent. This is a formal process, not just a signature on a form. The research team is required to explain the study’s purpose, how long it will last, exactly what treatments or procedures you’ll undergo, the known risks and potential benefits, what happens if you receive a placebo, and how your personal data will be protected. You can ask questions at any point, take the consent form home to review, and discuss it with family or your own doctor.
One detail that surprises many people: you can withdraw from a clinical trial at any time, for any reason, without consequences to your ongoing medical care. That right is built into every informed consent process.
Costs, Insurance, and Compensation
A common concern is whether joining a trial will create unexpected medical bills. Under the Affordable Care Act, non-grandfathered health plans and insurers cannot deny coverage of routine patient costs during an approved clinical trial for cancer or other life-threatening conditions. They also can’t impose extra conditions on that coverage or discriminate against you for participating. This has been in effect since 2014 and is self-implementing, meaning it doesn’t depend on additional regulations.
The experimental treatment itself is almost always provided at no cost by the study sponsor. What insurance covers are the “routine costs,” meaning the standard medical care you’d receive whether or not you were in the trial: doctor visits, lab tests, scans, and hospitalizations related to your condition.
Many trials also compensate participants for their time and inconvenience. International ethical guidelines state that compensation should be proportional to the time spent participating, including travel to the study site, and should use the regional minimum hourly wage as a reference point. Compensation can be monetary or non-monetary. Some trials offer gift cards, transit passes, or direct travel reimbursement. The key principle is that participation shouldn’t cost you money out of pocket. During your screening call, ask specifically what expenses are covered, whether travel is reimbursed, and whether there’s a stipend for each visit.
Questions Worth Asking Before You Commit
The screening call and consent process are your chance to get answers to practical questions that trial listings don’t always spell out. Four categories matter most: the study’s purpose and how long it lasts, what risks and potential benefits exist, what your day-to-day participation will look like, and what it will cost you personally.
Some specifics worth raising:
- Visit schedule: How often will you need to come in, and how long does each visit take?
- Placebo possibility: Is there a chance you’ll receive a placebo instead of the active treatment, and if so, what standard care will you still receive?
- Side effect management: What happens if you experience a side effect? Who do you call, and how quickly can you expect a response?
- Daily life impact: Will the trial require dietary changes, activity restrictions, or frequent blood draws that affect your work or routine?
- Results access: Will you be told whether you received the experimental treatment after the study ends, and will you have access to the results?
- Post-trial treatment: If the treatment works for you, can you continue receiving it after the study concludes?
You’re not obligated to say yes after a screening call, and a good study coordinator will encourage you to take time before deciding. Enrollment is voluntary at every step.