Every potential drug or treatment goes through several stages or “phases” of testing before it is available to the public. The first stages start small, and if things go well, the treatment is tested in larger groups with each phase. If the early phases of a trial show problems or safety issues, it may not progress beyond phase I or II.
Phase I purpose
Checks for safety and tries different levels or amounts of a potential treatment in a small group of volunteers.
Phase II purpose
Determines whether a treatment works for a specific condition and tracks different kinds of effects.
Phase III purpose
Confirms that the treatment works and monitors effects in a larger group. Compares the new treatment to existing ones (sometimes referred to as “treatment as usual” or TAU).
Phase IV purpose
Takes place after a treatment is approved and available to see how it works long-term when used in daily life.