Clinical trials have four research phases .
A Phase I study is the first use of a new drug or a new drug indication in humans. It is used to test for safety and side effects, and to determine how the drug should be given. Only a limited number of patients are accepted for participation in Phase I trials. If the Phase I trial shows safety, a Phase II trial is initiated to investigate the ideal dosing range of the drug. The therapy is tested in a larger number of patients to determine how well it works, and other possible, less common side effects.