What is a Clinical Trial?

For US residents only.

What is a Clinical Trial?

Clinical trials are medical studies that test new medicines. When you take part in a clinical trial, you’re helping doctors learn more about treating disease and improving health care for others.


How clinical trials are set up

Clinical trials often test new drugs or new combinations of drugs. They are usually organized into 4 phases. Each phase helps researchers answer different kinds of questions:

  • Phase 1 trials test an experimental drug, vaccine, or device with a small group of healthy people to learn about safety, including side effects, ways to take the drugs and what dosage is best

  • Phase 2 trials test new drugs with larger groups of people with a specific disease to learn more about safety and how well the drug works to treat their condition

  • Phase 3 trials test new drugs with even larger groups of people with a specific disease to confirm how well they work, learn more about safety, and sometimes compare it to similar treatments

  • Phase 4 trials, also known as postmarketing surveillance trials,are done after the US Food and Drug Administration (FDA) approves a drug to track safety in the general population and learn more about how it works and can be used


Who can join clinical trials?

Although every trial is different, researchers follow specific guidelines to determine who can participate in clinical trials. These guidelines are called eligibility criteria. These criteria not only show if you qualify for the clinical trial, but also help researchers see if the trial would be safe for you. Eligibility criteria often include the following:

  • The disease(s) or stage of disease(s)

  • Past treatments received

  • Age

  • Medical history

  • Current health


Every participant is required to get a physical check-up and set of clinical tests to confirm they are eligible for the trial.

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