What is a clinical trial?

Clinical trials are investigations to evaluate new ways to prevent, diagnose or treat diseases in human patients or healthy volunteers. They test medical devices, products or techniques, or they explore new ways of using existing treatments, or combinations of different treatments. Based on the results of clinical trials, scientists can evaluate treatments in relation to both safety and effectiveness. Clinical trials are launched when there is good evidence from laboratory (or other preliminary) studies to suggest that the intervention being tested is an improvement on the current best practice.

Clinical trials are sometimes referred to as ‘clinical studies’, ‘medical research trials’ or simply ‘trials’. Almost all the pharmaceuticals that we use today can be traced back to the results of clinical trials conducted in the past.


Normally, there are four phases in the clinical trial process, referred to as Phases I-IV. Each phase of a clinical trial has a different purpose and helps scientists to find answers to various questions.




is to test the safety and possible side effects of a new treatment or intervention, and to identify the best dose to administer.



 is to test if the treatment or intervention is effective against the disease and to find out more about the safety and dosage. 


 is to compare the new treatment with the current best practice and identify if it’s more effective. Phase III trials usually recruit large numbers of patients from many different sites because it can be difficult to compare the two categories of treatment with small groups. Patients are usually randomised, which means they are assigned to a treatment category (new treatment or current best practice) at random. 


 is usually carried out after an intervention has been approved for use. Phase IV trials are typically used to study if a treatment works for a wider range of uses, or to understand its long-term effects.