According to ClinicalTrails.gov, a service of the National Institutes of Health (NIH), “A clinical trial is a research study to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective.”
Clinical trials are conducted in four phases. Each phase has a different purpose and helps researchers answer different questions. The results of each phase are reported to the U.S. Food and Drug Administration (FDA) to assure that safe practices are being maintained and that the research study is being carried out appropriately. The FDA is responsible for determining if a drug is safe and effective before it can be prescribed.
NIH defines the four phases as follow:
In Phase I trials, researchers test an experimental drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
In Phase II trials, the experimental study drug or treatment is given to a larger group of people (100-300) to see if it is effective and to further evaluate its safety.
In Phase III trials, the experimental study drug or treatment is given to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely.
In Phase IV trials, post marketing studies delineate additional information including the drug's risks, benefits, and optimal use.
