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How to Find a Clinical Trial

The 4 Phases of Clinical Trials

Clinical trials are carried out in phases, each with a different purpose. Here’s a description of the different questions that scientists try to answer during each phase:

  • Phase I:An experimental treatment is given to a small group of people (usually 20 to 80). The goal is to understand the best way to deliver the new treatment, check its safety, find a safe dosage range, and identify side effects.
  • Phase II: The drug or treatment being studied is given to a larger group of people (100-300) to test its effectiveness and to further evaluate safety. At this stage, there may or may not be a control group. People in a control group receive standard care but not the experimental therapy; people in treatment groups get the experimental therapy. A control group allows the researchers to compare the new therapy to other treatment, a placebo, or no treatment.
  • Phase III:The researchers give the experimental drug or treatment to large groups of people (1,000-3,000) to confirm effectiveness, monitor side effects, make comparisons to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely. During this phase, there's usually a control group and a treatment group. People are randomly assigned to one of those groups; you can't choose which group you'll be in, and if there is a placebo group, you likely won't know if you're getting the placebo or the experimental therapy. 
  • Phase IV:This research phase takes place after the study drug or treatment has received FDA approval. These post-marketing studies gather additional information, including the drug's risks, benefits, and optimal use in a larger population.

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WebMD Medical Reference

Reviewed by Laura J. Martin, MD on July 03, 2012

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