Phase 0

Exploring if and how a new drug may work.

These are exploratory studies that often use only a few small doses of a new drug in a few patients. The phase 0 studies help researchers find out whether the drugs do what they are expected to do.

Phase 1

Is the treatment safe?

Phase I studies of a new drug are usually the first that involve people. These studies usually include a small number of people 920 to 80).

This will usually be the first time the medicine has been tried on humans, and therefore there’s an unavoidable element of risk.

Phase 2

Does the treatment work?

If a new treatment is found to be reasonably safe in phase I clinical trials, it can then be tested in a phase II clinical trial to look for evidence that it works. The medicine is tested on a larger group of people who are ill. This is to get a better idea of its effects in the short term

Phase 3

Is it better than what’s already available?

Phase III clinical trials compare the safety and effectiveness of the new treatment against the current standard treatment. They test in larger groups of people who are ill, and compare new medicine against an existing treatment or placebo.

Phase 4

Post marketing surveillance.

Phase four trials take place after all the previous stages have been passed and have been given marketing licences. The medicine can now be made available on prescription. The safety, side effects and effectiveness of the medicine continue to be studied while it's being used in practice.

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Clinical Trial Phases

The diagram below explains more about the different phases of Clinical Trials and Studies.

Phase 0

Phase 1

Phase 2

Phase 3

Phase 4