What is a clinical study?

A clinical study is a research study designed to answer specific questions about vaccines or new therapies or new ways of using known treatments.

Clinical studies (also called medical research and clinical trials) are used to determine whether new drugs or treatments are both safe and effective.  Carefully conducted clinical studies are the fastest and safest way to find treatments that work.

Ideas for clinical studies usually come from researchers.  Once researchers test new therapies or procedures in the laboratory and get promising results, they begin planning clinical trials.

Clinical trials proceed through four phases of testing:

• In phase I clinical trials, researchers test a new drug or treatment in a small group of people (approximately 20 - 80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
• In phase II clinical trials, the study drug or treatment is given to a larger group of people (approximately 100 - 300) to see if it is effective and to further evaluate its safety.
• In phase III clinical trials, the study drug or treatment is given to large groups of people (approximately 1,000 - 3,000 or more) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
• Phase IV clinical trials are done after the drug or treatment has been marketed.  These studies continue testing the study drug or treatment to collect information about their effect in various populations and any side effects associated with long-term use.