A clinical trial is a research study in people that tests a medical, surgical or behavioral intervention. The National Institutes of Health describes trials as the primary way researchers find out whether an intervention, such as an investigational drug, diet or medical device, is safe and effective in people (NIH: The Basics). An intervention being tested is called investigational until regulators have reviewed the evidence.
Interventional and observational studies
ClinicalTrials.gov lists two main study types (ClinicalTrials.gov glossary):
- Interventional studies (clinical trials) assign participants to receive an intervention, such as an investigational drug, a device, a procedure or a behavior change program, and measure what happens.
- Observational studies do not assign a treatment. Researchers follow participants and collect information, for example on symptoms or how a usual-care medicine works over time.
How a trial is designed
Every trial follows a written plan called a protocol. It sets out who can join, what happens at each visit, how long the study lasts and what will be measured. Common design features include:
- Randomization: participants are assigned to groups by chance so the groups can be compared fairly.
- Placebo or comparison groups: some participants may receive an inactive substance or the current standard treatment instead of the investigational one.
- Blinding: participants, and sometimes the researchers, do not know who is in which group until the study ends.
Eligibility criteria
Each study lists inclusion criteria (who can take part) and exclusion criteria (who cannot). These often cover age, sex, the stage of a condition, other health conditions and current medicines. They exist to protect participants and to make sure the results answer the research question. Some studies also accept healthy volunteers, people without the condition being studied. The study team makes the final decision on eligibility, usually after a screening visit.
Oversight and informed consent
In the United States, studies of FDA-regulated products must be reviewed by an Institutional Review Board (IRB), an independent committee that checks that risks are minimized and reasonable (21 CFR Part 56). Before you take part, the study team must explain the study and obtain your written informed consent (21 CFR Part 50). The consent form describes the purpose, procedures, foreseeable risks, possible benefits, alternatives and any payment.
Taking part is voluntary. Federal rules require the consent form to state that you can leave a study at any time without penalty or loss of benefits you are otherwise entitled to.
Questions to ask the study team
The FDA suggests asking questions before you decide (FDA: Clinical Trials, What Patients Need to Know). Useful ones include:
- What is the purpose of the study, and what phase is it in?
- What tests, visits and procedures are involved, and how much time will they take?
- What are the possible risks and side effects?
- Will I be told which group I was in when the study ends?
- Will any costs be covered, and is compensation for time and travel available?
- What happens if I am harmed, or if I decide to leave the study?
Talk with your own doctor before joining a study. To learn what the phase on a listing means, read clinical trial phases explained.
Source: ClinicalTrials.gov, data processed . Recruiting US sites filtered by distance and site status; summaries shortened.