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Phases of Clinical Trials

Phases of Clinical Trials

According to the National Cancer Institute, most clinical research that involves the testing of a new drug progresses in an orderly series of steps, called phases. This allows researchers to ask and answer questions in a way that results in reliable information about the drug or device and protects the patients. Clinical trials with drugs are usually classified into one of three phases:


Phase I trials : These first studies in people 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.  A Phase I trial usually enrolls only a small number of patients, sometimes as few as a dozen.

Phase II trials : A Phase II trial continues to test the safety of the drug and begins to evaluate how well the new drug works against a specific condition or conditions.

Phase III trials: These studies test a new drug, a new combination of drugs, or a new surgical procedure in comparison to the current standard. A participant will usually be assigned to the standard group or the new group at random (called randomization). Phase III trials often enroll large numbers of people and may be conducted at many doctors' offices, clinics, and research centers nationwide.

Phase IV trials:  Phase IV trials are done after a drug has shown to work and has been granted a license from the U.S. Food & Drug Administration. So investigators are looking at drugs that already are available for physicians to prescribe, rather than new drugs that are still being developed.