A clinical trial, also called a clinical study, is a research study designed to answer specific questions about new medical approaches (e.g. drugs, therapies) or new ways of using existing approaches. These studies can test screening methods as well as prevention, diagnosis or treatment of a condition or disease. A clinical trial is one of the final steps in the research process. Health professionals run clinical studies according to strict guidelines set by the Food and Drug Administration (FDA) to ensure that people who agree to be in the studies are treated as safely as possible. Clinical trials are usually conducted in four phases with patients to evaluate the effectiveness of new medical approaches. The FDA requires strict testing of all drugs and vaccines prior to their approval for use as therapeutic agents in the general population.