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What Are Clinical Trials?

Overview of Phases for Clinical Trials

Phase 1:

Researchers test a new drug or treatment in a small group of healthy volunteers and/or people with the disease for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. Purpose: Safety and Dosage

Phase 2:

The drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety. Purpose: Efficacy and Side Effects

Phase 3:

The drug or treatment is given to large groups of people 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. More than one Phase III study may be required before a New Drug Application (NDA) may be submitted to the FDA. Purpose: Efficacy and Adverse Reactions

FDA Approval

Phase 4:

Studies are done after the drug or treatment has been marketed to gather information on the drug’s effect in various populations and any side effects associated with long-term use. Purpose: Safety and Efficacy

View a 2-part series on the ABC's of Clinical Trials


Choosing to participate in a clinical trial is an important personal decision. It is often helpful to talk to a physician, family members, or friends about deciding to participate in a clinical trial. The following frequently asked questions provide an overview of clinical trials.

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