Clinical Trials Explained for Participants
A plain guide to joining a clinical trial in the United States: what consent must cover, what phases mean for you, your right to leave, and why a trial listing is not an endorsement.
Content last updated . This page has not been medically reviewed.
What a trial is and is not
- A trial tests whether a product is safe and effective for a stated use. It may involve a placebo or an approved comparison treatment; see Randomization, Blinding and Placebo.
- Some trials need healthy volunteers to help answer research questions. [1]
- A listing in ClinicalTrials.gov, or a firm's registration with the FDA, does not mean a product is legally marketed. [2] A listing also says nothing about whether the treatment works. See Registered Trials vs Published Results.
- You can look for studies at ClinicalTrials.gov, and the FDA suggests talking to your health care provider. [1]
What the phases mean for you
The FDA describes the usual sequence. [3]| Phase | What happens | What it means for you |
|---|---|---|
| Phase 1 | Researchers test a new drug in healthy volunteers, or in people with the condition | Early, closely monitored; aims at safety and dosage |
| Phase 2 | Typically a few hundred patients | Not large enough to show whether the drug will be beneficial |
| Phase 3 | Designed to show whether a product offers a treatment benefit to a specific population | Larger; more safety information |
Before a trial starts, the sponsor submits an IND and must wait 30 calendar days before starting. [4] The FDA can also place a clinical hold to delay or stop an investigation. [3] More detail: Clinical-Trial Phases Explained.
Informed consent: what you should be told
You should have the study explained to you in an informed consent process before you agree to join. [1] Under U.S. rule 21 CFR 50.25, the information given to each participant includes: [5]- That the study involves research, its purpose, how long you would take part, and the procedures, including any that are experimental.
- Any reasonably foreseeable risks or discomforts.
- Any benefits to you or others that may reasonably be expected.
- Alternative procedures or courses of treatment that might be advantageous to you.
- How confidentiality of your records is handled, and that the FDA may inspect the records.
- For research with more than minimal risk, whether compensation or medical treatment is available if you are injured.
- Whom to contact with questions about the research and your rights, and about a research-related injury.
- That taking part is voluntary, and that refusing involves no penalty or loss of benefits to which you are otherwise entitled. [5]
When appropriate, you should also be told that a treatment may involve currently unforeseeable risks, and about any additional costs to you. [5] The consent form also identifies the Institutional Review Board (IRB), the group that assures protection of participants' rights and welfare. [6] For more, read Informed Consent in Emerging Treatments.
Questions worth asking
- What is being tested, and what stage is it?
- What happens if I get a placebo or a comparison treatment?
- What are the known and unknown risks, and who treats me if something goes wrong?
- Are there approved or other options I should compare?
- What will it cost me, and who pays for study-related care?
- Who do I call with concerns, and what happens if I leave?
Why representation matters
The FDA says people from underserved communities are underrepresented in clinical research, and that people of different ages, races and ethnicities may react differently to medical products. [1]Red flags
Being charged for an unapproved product, or told a "trial" is a way to buy a treatment, calls for caution. The FDA says that for regenerative medicine products offered outside a clinical trial, being charged means you are likely being deceived and offered a product illegally. [2] See Research Participation and Therapeutic Misconception. To report a reaction to an FDA-regulated product, see Adverse-Event Reporting for Emerging Products.Frequently asked questions
Can I leave a trial after I sign?
Yes. Participation is always voluntary and you can leave a study whenever you want. [1]
Does joining a trial guarantee I get the new treatment?
No. Trials answer research questions, and a product may or may not work. [1] Ask whether a placebo or comparison treatment is used.
Who protects participants?
An Institutional Review Board assures the protection of the rights and welfare of human subjects, and the consent form identifies it. [6]
Is a registered trial proof the treatment works?
No. Registration shows a study exists; the FDA says it does not mean a product is legally marketed. [2]
What if I cannot join a trial?
For serious or immediately life-threatening conditions with no satisfactory alternative, a regulated route exists. See Expanded Access ("Compassionate Use"). [7]
References
- U.S. FDA, Clinical Trial Participation (page current as of 12/05/2024). Read 2026-10-22.
- U.S. FDA, Important Patient and Consumer Information About Regenerative Medicine Therapies (posted June 3, 2021; page current as of 04/08/2024). Read 2026-10-22.
- U.S. FDA, The Drug Development Process, Step 3: Clinical Research (page current as of 01/04/2018). Read 2026-10-22.
- U.S. FDA, Investigational New Drug (IND) Application. Read 2026-10-22.
- Electronic Code of Federal Regulations, 21 CFR 50.25, Elements of informed consent. Read 2026-10-22.
- U.S. FDA, Public Safety Notification on Exosome Products (December 6, 2019). Read 2026-10-22.
- U.S. FDA, Expanded Access (page current as of 10/22/2026). Read 2026-10-22.