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Phases of Clinical Trials

The four phases of clinical trials are:

  • Phase I: These trials are the first stage of testing in human subjects. Normally, a small (20–100) group of healthy volunteers is selected. This phase includes trials designed to assess the safety of a drug, procedure, or device (the treatment). In Phase I trials, little is known about the treatment’s effectiveness in people.
  • Phase II: Once the initial safety of the study treatment has been confirmed in Phase I trials, Phase II trials are performed on larger groups (20–300) to test the effectiveness (efficacy) of the treatment. When the development process for a new treatment fails, this usually occurs during Phase II trials when the treatment is discovered to not work as planned. When the benefits of treatment outweigh side effects and/or risks, the next phase of testing can begin.
  • Phase III: These studies are randomized, controlled, multi-center trials on large patient groups (300–3,000). The trials in this phase are aimed at being the definitive assessment of how effective the treatment is in comparison with the current standard proven treatment.
  • Phase IV: These trials are also known as Post Marketing Surveillance Trials. Phase IV trials involve the safety surveillance and ongoing technical support of a FDA-approved drug, device, or procedure. Phase IV studies may be required by the FDA or may be undertaken by the sponsoring company (manufacturer). An example of this type of study is the study of aspirin, which was initially approved as a pain reliever, but was later found to be useful as a blood thinner.
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