Clinical trials are research studies designed to answer specific questions about investigational drugs that may benefit future patients and current research participants. The trials are designed to assess both the safety and effectiveness of new drugs in humans.

Clinical trial is conducted in phases. There are four phases (Phase I, II, III and IV) of clinical trial, each phase with different purposes and durations. Phase I trials generally involve healthy volunteers whilst Phase II, III and IV trials involve patients with diseases.

At each phase, researchers try to answer different questions about the new drug they are investigating. Progression from one phase of a clinical trial to the next phase generally requires success in the prior phase.