Phase I trials are the first set of studies performed in humans that begin following extensive animal studies. The goals of the trial investigators are to monitor safety and become aware of unknown risks. Phase I Trials are offered to a small group of subjects for conditions in which no treatments currently exists.

Phase II trials test the effectiveness or response of a treatment or intervention on a group.  Phase II trials are conducted with a larger group of subjects than Phase I, but still with a small number of patients due to unknown risks.  These trials provide more opportunity to discover less common side effects of a treatment.

Phase III trials are the final phase of trials before the treatment is approved by the Food and Drug Administration (FDA) and involve a larger number of subjects.  These trials test the new treatment against the standard treatment for the disease/condition.

If all the phases are completed and the treatment being tested proved to be more effective and/or safer than the current treatments available, the FDA will approve the treatment and the treatment then becomes standard therapy.  This process takes years and hundreds of volunteers are needed.

Even after FDA approval, additional information is needed on the effectiveness or the safety of a new treatment. If so, a Phase IV clinical trial is conducted to provide such information.