Phases of a Clinical Trial

Clinical trials are conducted in four different phases, with each phase designed to answer a specific research question.

Phase I Trials evaluate how a new drug should be given (by mouth, injected into the blood, or injected into the muscle), how often, and what dose is safe.

Phase II Trials continue to test the safety of the drug, and begins to evaluate how well the new drug works. Phase II studies usually focus on a particular type of cancer.

Phase III Trials compare a promising new drug, combination of drugs, or procedure, with a current standard of treatment. A participant will usually be assigned to the standard group or the new group at random. Phase III trials often enroll large numbers of people and may be conducted at many doctors' offices, clinics, and cancer centers nationwide.

Phase IV Trials include the continuing evaluation that takes place after FDA (Food and Drug Administration) approval, when the drug is already on the market and available for general use (post-marketing surveillance).