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Steps of a Clinical Trial

Enrolling in a Clinical Trial

Clinical research to test a new treatment is a long process that requires many steps. Each step is important so researchers can learn if a treatment is effective, if it is safe for patients, and how it compares to current treatments. The research process must also protect the rights and welfare of patients. 

Phases of Clinical Trials

Clinical trials follow a series of steps or phases. The research goals and plans are different depending on the phase of study.

Phase I

Phase I clinical trials test new treatments that are being studied for the first time. In this phase, a small number of people receive the experimental treatment. A main goal of this phase is to find out if the treatment is safe and to get information on the dose that should be used.

Questions answered by Phase I

  • Is the treatment safe?
  • What dose of the treatment should be given?
  • What are the side effects of the treatment?

Phase II

Phase II trials test the experimental treatment in more people for a longer period of time. The goal is to find out if the treatment works for people with a certain disease or condition. Side effects are monitored.

Questions answered by Phase II

  • What is the effect of treatment on a disease or condition?

Phase III

Phase III trials test the treatment in a large number of people. The experimental treatment may be compared against a standard treatment, or two different experimental treatments may be compared to each other. Side effects are monitored over a longer period time.

Questions answered by Phase III

  • How does the new treatment compare to a standard treatment?

Phase IV

Phase IV trials test the treatment in a very large number of people after the drug or device has been approved by the U.S. Food and Drug Administration (FDA). Researchers collect information about how the treatments are used and monitor side effects and effectiveness over long periods of time in a large number of patients.

Questions anwered by Phase IV

  • What are the effects of treatment in different people over time?
  • What are the long-term benefits?
  • What are the long-term risks?
  • How is the new treatment incorporated into medical care?

Reviewed: June 2018