Clinical trials
What phases mean
A phase describes the main purpose of a medicine study. It is one part of the information you should consider, not a quality ranking.
Early phase and Phase 1
These studies usually look at how a treatment is given, how the body responds and what dose may be appropriate. They often involve a smaller number of people.
Phase 2
These studies continue to look at safety and begin to explore whether the treatment has the intended effect. Different Phase 2 studies can have different designs.
Phase 3 and Phase 4
Phase 3 studies often involve more people and compare a treatment with another treatment or usual care. Phase 4 studies take place after approval and continue to collect information about use and safety.