Phases of a clinical trial

Phase I

Phase I tests a small group of healthy volunteers to see how safe a new treatment is and what the right dose should be.

Phase II

Phase II tests whether the treatment is effective and safe in a larger group of people with a specific disease.

Phase III

Phase III tests the treatment in even more people with a specific disease in different parts of the world. This is usually the last step before approval (marketing authorization).

Phase IV

Phase IV studies take place after a treatment has been approved and are designed to gather more information about the treatment over a longer period.