The University of Iowa

What are the Phases of Clinical Trials?

Most discoveries of new treatments are the result of laboratory experiments. When researchers are ready to evaluate a new treatment in people, they carefully design clinical trials to test the treatment''s effectiveness, its safety, and its side effects. Clinical trials follow an orderly progression of steps or phases to take the medication or other type of treatment from discovery to approval by the Food and Drug Administration (FDA).

Phase I Trials

The very first trials to evaluate a new treatment may involve people without the illness or condition (healthy volunteers), or they may involve those who have the condition. Phase I clinical trials evaluate how a new treatment should be given (for example, orally or by injection), how often, and in what dose.

Phase II Trials

A phase II trial, which involves people with a particular illness or condition, provides preliminary information about the benefit and safety of the new treatment.

Phase III Trials

These trials are designed to compare the effectiveness and safety of the new medication or treatment with treatments already available for general use. Patients participating in Phase III trials are likely to be assigned by chance (randomized) to receive one of the following:

  • the new medication/treatment
  • the standard medication/treatment
  • an inactive substance called a placebo

Most of these trials are designed so that neither the participants nor the researchers know which treatment is being given to a particular individual. This is done so that the effects of the treatment are reported fairly.

Phase III trials involve hundreds or thousands of patients nationwide or even worldwide. If the results of a Phase III trial are favorable for the new treatment, then FDA approval will be sought. Once aproved by the FDA, a treatment will be available to the general public.

Phase IV Trials

At times, even after FDA approval, additional information is needed on the effectivness or the safety of a new treatment. If so, a phase IV clinical trial is conducted to provide such information.

Other Trials

Other supportive care, prevention, and screening trials are not done in phases, but instead compare groups of people using another strategy (counseling, behavior changes, detection method) with those who do not.