Most clinical trials are designated as phase I, II, III, or IV, based on the type of questions
that study is seeking to answer:
In Phase I clinical trials, researchers 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 Phase II clinical trials, 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 Phase III clinical trials, 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
In Phase IV clinical trials, post marketing studies delineate additional
information including the drug's risks, benefits, and optimal use.
These phases are defined by the Food and Drug Administration in the Code of