Clinical trials are conducted in phases. Each phase of a trial has a different purpose and helps scientists to answer specific questions.
While small, early phase trials may be conducted by individuals or small groups of physicians, larger trials are typically conducted by hospitals, pharmaceutical companies, or device manufacturers. If a therapy successfully passes through Phase III trials, the FDA may approve it to be marketed to the public.
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Phase |
Definition |
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Phase I Trials |
Researchers test a new drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. |
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Phase II Trials |
The study drug or treatment is given to a larger group of people (100-300) to see if it is effective, and to further evaluate its safety. |
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Phase III Trials |
The study drug or treatment is given to large groups of people (1000-3000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely. |
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Phase IV trials |
Postmarketing studies delineate additional information including the drug’s risks, benefits, and optimal use. |