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How Are Clinical Trials Conducted?

Clinical trials testing new treatments are carried out in phases.

  • Phase I — Is the Treatment Safe?
    As the first step in testing the research, doctors gather information about the side effects of the treatment and decide on the safe dose. Only a few patients in a few places take part in a Phase I trial.
  • Phase II — Does the Treatment Work?
    In this step, doctors test the treatment to see how well it works. Most of the time, fewer than 100 patients are involved in Phase II trials.
  • Phase III — Is the Treatment Better?
    Phase III trials compare the new treatment against the current standard therapy and randomly assign patients into one of the two groups. Many people from all over the country take part in these trials.
  • Phase IV — Are There Better Ways to Use the Treatment?
    In this final step, treatments are tested to make sure they are safe and work well over a long period of time. This phase most often occurs once the new treatment has been approved for standard use. Anywhere from several hundred to several thousand people are enrolled in a Phase IV trial.