What are Phase 3 clinical trials?


Treatments only move into a Phase 3 clinical trial if phases 1 and 2 suggest that a substance might actually be useful and safe in ways that patients would regard as important. Phase 3 trials test new drugs in larger groups of people who are ill. Phase 3 trials compare the new drugs with whatever treatments are currently in use, or occasionally with a placebo. These trials look at how well the new treatment works in practice, and at any side effects. They usually last longer than phase 2 trials – typically a year or more. Often several thousand patients in different countries will be involved in a phase 3 trial. A large number of participants is necessary because investigators have to be able to detect moderate but important differences between treatments.