Once a new medical treatment has shown promise in laboratory tests, it has to pass three key stages of clinical trials before it can be officially approved for use. The three stages are:
• Phase I trials
• Phase II trials
• Phase III trials
Phase I trials
Phase I trials focus on the safety of a new medical treatment. They involve only a small number of people, who are usually healthy volunteers. The trials look at several measures of safety, such as side-effects of the treatment.
Phase II trials
Phase II trials focus on whether the treatment is effective. They generally involve a larger group of volunteers than phase I trials. The volunteers are usually patients who have the condition the treatment is intended for. Phase II trials also look at safety.
Phase III trials
Phase III trials focus on the specific benefits of the new treatment by comparing it with a similar treatment or a placebo (a ‘dummy’ treatment). Patients who receive a placebo should still also receive the best standard care. Phase III trials last longer than phase I or II trials (usually a year or more) and involve more people (often several thousand treated across different hospitals in different countries).
You can find more information about the terms used in clinical trials in our research glossary.
