What are clinical trials?

A clinical trial is the name given to the process whereby the safety of medical treatments for use on humans is assessed.

All new medical treatments (such as drugs, medical devices and technical procedures) need to go through clinical trials to ensure that they are safe and effective for use on patients.  Clinical trials involve testing the treatments on humans.

It takes many years to develop a new medical treatment from the laboratory to use in the clinic on patients.  Before being tested on humans, the drug is extensively tested: first on cell cultures and then on animals to assess whether the treatment is safe to test on humans.  If it passes these tests it then goes through a number of critical stages:

  • Phase 1.  This is where the treatment is tested on a small number of people who don’t necessarily have the condition that the drug is designed to treat.  The aim of this phase is to find out whether the drug is safe and how much of the drug should be given.
  • Phase 2.  This is where the treatment is given to a larger number of people with the condition that the drug is designed to treat.  This phase is designed to test whether the drug is effective against the particular condition, what dose should be given to treat the condition and to assess for any side-effects.
  • Phase 3. This is where the treatment is given to hundreds to thousands of people.  This phase is designed to test for effectiveness compared to current treatments and gather information on any rarer side-effects.

Only a small percentage of treatments that enter phase 1 trials actually complete the process and become available for treatment.  If the drug passes all these three phases, the manufacturers can apply for licences in each country so that the drug can become available to doctors to prescribe to patients.  However, long-term studies are still carried out to monitor the drug’s effectiveness, the frequency of side-effects and any longer-term effects.

You can find out more information about how clinical trials work and how to find out about clinical trials currently underway at the links below. 

Last reviewed: May 2022