The Center for Pharmaceutical Research -- Tomorrow's Medicines Today

What is a Clinical Trial? Clinical trial process and phases


Before a pharmaceutical drug can be approved by the FDA for use in the United States, it must go through several phases of testing, called clinical trials.

During the clinical trial process, the potential drug is tested for safety and effectiveness. Volunteers are followed very closely by the doctor running the trial, called the Principal Investigator. Most clinical trials require regular office visit and more frequent medical test such as blood draws, ECGs, or physical exams. In addition, patients are often asked to keep careful record of changes to their health.

After receiving permission from the FDA, the clinical trials begin. Each drug goes through the following phases of testing:

  •   Test the drug in humans for the first time.
  •   Usually include only healthy volunteers.
  •   Primarily test for safety.
  •   Commonly require overnight stays.
  •   Focus on proving the drug's effectiveness
  •   Only begin after the drug has been proven safe in humans.
  •   Include a more people than phase I studies.
  •   Compare various doses of the study drug with placebo.
  •   Begin when the drug has passed the phase II safety and effectiveness trials.
  •   Are often the final step prior to FDA approval.
  •   Provide a more thorough understanding of the drug's effectiveness, benefits, and possible adverse reactions.
  •   About 75% of new drugs get to this stage.
  •   Gather long-term or marketing data.
  •   Often occur after the drug has been approved by the FDA.

Ninety-percent of drugs that reach Phase III go on to final evaluation by the FDA to seek approval for public use. Though the process takes many years, the end result of new, more effective treatments options makes the effort worthwhile.