Phases of Clinical Trials

Clinical trials mostly occur in four phases.
Phase 1: Screening for safety
Phase 2: Establishing the testing protocol
Phase 3: Final testing
Phase 4: Postapproval studies

Phase 0:
Laboratory and animal testing. This is done to understand the potential of the new approach and its possible success in humans.

Phase 1:
It is done to test the new approach in humans and hence is done in a small population. The subject sample size can range from 20 to 100 depending of the extent of the study. The process involves lab tests to determine the effect of the new approach and its benefits to the patients. It is also used to determine the safe usage criteria and side effects, if any, for using the new agent in Phase 2.

Phase 2:
It is done in a larger population, 20 - 300 people. The new approach is tried in groups of people suffering from a disease/condition under the safety criteria found in Phase 1. If the new approach proves to be effective and safe, it enters Phase 3.

Phase 3:
The new approach is now introduced to large groups of people (300-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow it to be used safely. Randomization is used to maintain validity of the data.

Phase 4:
The last phase of clinical studies is done after the device is approved and marketed. It is done to obtain additional information on the optimal use, risks or benefits of the new approach.