A clinical trial is a research study designed to answer specific questions about new drugs, medical devices, or new ways of using known treatments. Clinical trials are used to determine whether the new drug or treatment is safe, and whether it works.
Clinical trials consist of four phases:
Phase I tests a new treatment on a small group, and concentrates on safety;
Phase II deals with safety and efficacy, and expands the study to a larger group of people (several hundred);
Phase III expands the study to an even larger group of people (thousands), and is designed to determine conclusively whether or not the treatment is effective;
Phase IV takes place after the drug has been licensed, to monitor the drug for long-term effects.