Definitions of Phases
Phase I
a relatively small number of healthy volunteers are treated to test the safety of a new drug.
Phase II
selected patients showing a number of common features, such as age, sex and severity of the disease participate in trials to establish the effectiveness of the drug.
Phase III
large numbers of patients from the ‘clinical setting’ who are widely representative of the patient population are enrolled in the trial. Patients come from all walks of life, often from a number of participating centres. The aim of Phase III trials is to determine whether a new treatment is any better than the standard treatment in a direct comparison of the two.
Phase IV
Phase IV trials are done after a drug has been shown to work and has been granted a license. These trials look at drugs that are already available for doctors to prescribe, rather than new drugs that are still being developed. The main reasons pharmaceutical companies run phase IV trials are to find out more about the side effects and safety of the drug, what the long term risks and benefits are how well the drug works when it’s used more widely than in clinical trials.
