Participating in Clinical Trials

Frequently Asked Questions

13. What are the phases of a clinical trial? - cont'd

A Phase II trial is similar to a Phase I trial but uses more people (100 to 300) to find out if the experimental treatment is effective and safe. This phase can last several years.

A Phase III trial is a large study using several hundred or more participants (1,000 to 3,000). This phase compares the experimental drug or procedure to a placebo or standard treatment, to make sure it is safe and works well. Some side effects that didn't show up in Phase II may show up in a Phase III trial because many more people are tested.

If the U.S. Food and Drug Administration agrees that the trial results are positive, they will approve the experimental drug or device.

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