What Are the Different Phases of Clinical Trials?

Clinical trials are divided into phases created to gather specific information about the treatment or drug being studied. Four phases, or stages, are used and each phase is designed to build on the phase preceding it. The four phase clinical trial will determine safety, whether the treatment or drug works, if this is an improvement on what is presently available, and if there are any additional uses and benefits.

Phase l

• In the Phase l trials, a small group of people -- about 20 to 80 -- are used for the first time. Preclinical studies have already been done on animals and in petri dishes. The experimental treatment or drug will be evaluated for safety, to determine the safe dosage range, and to determine side effects. In this phase, researches will determine whether it is best to give the treatment in pill form or as an injection, and what is the highest dosage that can be given without side effects. Participants are closely monitored, so the dose can be adjusted. The determined dose is generally what is used for additional testing.

Phase ll

• In the Phase ll trials, a larger group of people -- approximately 100 to 300 -- are used. Based on the results of Phase l, the method of giving treatment will now be used and checked with the new participants for effectiveness and a further evaluation of safety. If a determined amount of participants benefit from the new treatment with acceptable side effects, the clinical trial will then go on the Phase lll.

Phase lll

• In the Phase lll trials, a much larger group will participate -- approximately 1,000 to 3,000. The effectiveness of the experimental treatment or drug will be confirmed, side effects will be monitored, a comparison will be made to other commonly used treatments, and information will now be collected to allow the experimental treatment or drug to be used. Phase lll may be double-blinded, according to the Breast Cancer website; the participants and the researchers will not know who is getting which treatment. This is the last step before the new drug is considered for approval by the U.S. Food and Drug Administration (FDA).

Phase lV

• The Phase lV trials are conducted after the treatment or drug has been approved by the U.S. Food and Drug Administration and is now on the market. Phase lV usually involves a large number of people and is in place to determine if there are side effects that were not apparent during Phase lll trials. Additionally, this phase will evaluate new benefits or uses for the new treatment or drug.