How Do Trials Work?

Phase one trials aim to test the safety of a new medicine.

A small number of people, who may be healthy volunteers, are given the medicine and researchers test for side effects and calculate what the right dose might be to use in treatment (known as dose-ranging studies).

Phase two trials test the new medicine on a larger group of people who are ill, to get a better idea of whether it works and how well it works in the short-term.

Phase three trials are only for medicines that have already passed phases one and two. They test medicines in larger groups of people who are ill, and compare a new medicine against an existing treatment or a placebo to see if it works better in practice and if it has important side effects.

Phase three trials often last a year or more and involve several thousand patients.

Phase four trials take place once new medicines have passed all the previous stages and have been given marketing licences. A marketing licence means the medicine can be made available on prescription.

In phase four trials, the safety, side effects and effectiveness of the medicine continue to be studied while it is being used in practice. Phase four trials are not required for every medicine.

Clinical Trials can be many different lengths. You may be asked to stay at our Unit for 3 or 4 days with one outpatient follow up approximately one week later, or you may be asked to participate in a trial which involves 20 days in our Unit.

We sometimes have outpatient studies where no overnight stays are required. Check out our volunteer’s stories for more information.