The clinical research process. (Resources).

The clinical testing of experimental drugs is normally done in three phases, each successive phase involving a larger number of people. Additionally, once the FDA has granted a New Drug Approval (NDA), pharmaceutical companies also conduct post marketing or late phase III/phase IV studies.

Phase I

Phase I studies are primarily concerned with assessing the drug's safety. This initial phase of testing in humans is done in a small number of healthy volunteers (20 to 100), who are usually paid for participating in the study. The study is designed to determine what happens to the drug in the human body--how it is absorbed, metabolized and excreted. A phase I …