Would you define clinical trial phases?

Phase I Trials: Primarily concerned with the drug's safety. Done on Healthy subjects and its the first time studied in humans. Amount of subjects to be used is approximately 20-100. Done in a hospital setting so side effects can be monitored more closely. Phase II Trials: Once tested in healthy subjects, its time to be done on the diseased subjects in which the drug is intended to cure or help. They are randomised studies as well in which case its usually blinded to all involved in the study and a Placebo is used. Several hundred subjects are tested and the company is concerned here with safety and efficacy of the drug. Lasts for about several months to a few years. Phase III Trials: Several hundred to several thousand subjects are needed for ph. 3 trials. Usually safety and efficacy again are involved to check more closely though, on severity of the adverse events. These studies can last years. Looks at study benefits, risks, etc. Phase IV Trials: Phase IV involves marketing the drug. Once the study is ended in Phase III, the study needs to be marketed. The FDA is notified of the end and results and the company applies then for the NDA (new drug application). The marketing is done for the public and looks at long term safety.