Phases of Clinical Trials

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There are usually four phases in the clinical trials process, each with a specific purpose and to help researchers answer certain questions:

• In a Phase I trial, investigators test a new drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
  
• In a Phase II trial, the study drug or treatment is given to a larger group of people (100-300) to see if it is effective and to further evaluate its safety.
  
• In a Phase III trial, the study drug or treatment is given to large groups of people (1,000-3,000) 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.
  
• Even after a drug has been released to the general public, additional studies continue as Phase IV trials. These post-marketing studies help to gather additional information including the drug's risks, benefits, and optimal use.