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Phases in drug developement


Phase I studies

The first stage in testing a new drug in humans. Usually performed on healthy volunteers without a comparison group.

Phase II studies

Second stage in testing a new drug in humans. These are often randomised controlled trials, and often performed in patients with the condition of interest. Typically they will be studies of shorter duration, or will examine dose-response relationships.

Phase III studies

Studies that are a full-scale evaluation of treatment. After a drug has been shown to be reasonably effective, it is essential to compare it to the current standard treatments for the same condition. Phase III studies are usually randomised controlled trials, and are of longer duration, and larger than phase II studies.

Phase IV studies

Studies that are concerned with post-marketing surveillance. They are often promotional exercises aimed at bringing a new drug to the attention of a large number of clinicians, and may be of limited scientific value. Phase IV studies may also be conducted in slightly different populations for license extensions.