ClinicalTrials.gov - Information on Clinical Trials and Human Research Studies

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Study Phase
Most clinical trials are designated as phase I, II, or III, based on the type of questions that study is seeking to answer:

In Phase I clinical trials, researchers test a new drug or treatment in a small group of people (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 (100-300) to see if it is effective and to further evaluate its safety.

In Phase III studies, the study drug or treatment is given to large groups of people (1,000-3,000) 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.

These phases are defined by the Food and Drug Administration in the Code of Federal Regulations.
Click the check box to the left of each study phase that you wish to include in your search. Select one or more study phases. If you do not select a specific phase, trials in any phase that match your other search terms will be retrieved.

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National Institutes of Health, Department of Health & Human Services