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Understanding clinical study phases

Clinical studies are classified under four phases:


Phase l: Researchers test an investigational drug in a small number of people by giving it to either healthy volunteers or patients to evaluate its safety, determine a safe dosage range and identify side effects.

Phase ll: The investigational drug is given to a larger number of people who have a particular disease or condition to further evaluate its safety and often to assess its effectiveness.

Phase lll: Several hundred to several thousand people with the appropriate disease or condition participate in these studies. The investigational drug undergoes additional testing to further determine its safety and effectiveness, monitor side effects, and compare it to commonly used treatments or placebo.

Phase lV: After a drug is available by prescription, additional information about a drug's risks, benefits and use may be gathered.