Clinical trials are research studies in which people help doctors find ways to improve health. Each study seeks to answer scientific questions and to find better ways to prevent, diagnose, or treat disease. Medical products, such as drugs, vaccines, and diagnostic tests, have to be studied in clinical trials before they can be approved for public use. A clinical trial follows a plan or “protocol” that is reviewed and approved before the trial can begin. This review ensures, among other things, that the trial follows appropriate safety guidelines.