Clinical research is usually designed to evaluate a drug, biologic or device in human subjects with the intent to discover potential beneficial effects and/or determine its safety and efficacy. Volunteers for drug trials are likely to get involved in one of four types of clinical trials:
Phase 1
Phase 1 trials are primarily designed to determine a drug's toxicity, and are limited to a small group of volunteers (typically less than 50).
Phase 2
Phase 2 trials are designed to test efficacy and safety of a drug in a larger but limited number of volunteers (100's) that have a particular disease or condition.
Phase 3
Phase 3 is for clinical drug trials designed to compare or determine additional evidence of efficacy in a larger group of people. It is usually the final phase of testing prior to FDA approval of an investigational drug.
Phase 4
Phase 4 trials are a post-marketing study of an FDA-approved drug focusing on the incidence of specific adverse reactions or long-term effects of the drug on morbidity and mortality.