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ClinicalTrials.gov - Clinical Trial Phases

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Clinical trials are conducted in a series of steps, called phases - each phase is designed to answer a separate research question.

• Phase I: Researchers test a new drug or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
  
  
• Phase II: The drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.
  
  
• Phase III: The drug or treatment is given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
  
  
• Phase IV: Studies are done after the drug or treatment has been marketed to gather information on the drug's effect in various populations and any side effects associated with long-term use.
  
  

Additional Resource Information on clinical trials can be found at http://clinicaltrials.gov/info/resources

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http://www.nlm.nih.gov/services/ctphases.html

Last reviewed: 18 April 2008
Last updated: 18 April 2008
First published: 01 January 2001
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