All clinical trials have criteria–or guidelines–about who can participate in the study. Guidelines are based on such factors as age, type of disease, medical history, and current medical condition. Before joining a clinical trial, a person must qualify for the study. Some research studies seek volunteers with illnesses or conditions to be studied in the clinical trial, while other trials need healthy volunteers.

Clinical trials are sponsored by: government agencies such as the National Institutes of Health (NIH); pharmaceutical companies; individual physician-researchers; health care institutions such as health maintenance organizations (HMOs); and companies that develop medical devices or equipment. Trials can take place in a variety of locations, such as hospitals, universities, doctors’ offices, or community health clinics.

A clinical trial is a research study designed to answer specific questions about new therapies, diagnostic tests, screenings, and disease prevention by testing new procedures in people. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are the fastest and safest way to find treatments that work.

Ideas for clinical trials usually come from researchers. Once researchers test new therapies or procedures in the laboratory and get promising results, they begin planning trials to test the therapy in people. New therapies are tested on people only after laboratory and animal studies show promising results.

Every clinical trial in the U.S. must be approved and monitored by an Institutional Review Board (IRB) to make sure the risks are as low as possible and are worth any potential benefits. An IRB is a committee of physicians, statisticians, patient advocates, and others that ensures that a clinical trial is ethical and the rights of study participants are protected. All institutions that conduct or support medical research involving people must, by federal regulation, have an IRB that initially approves and periodically reviews the research.

Informed consent is the process of learning the key facts about a clinical trial before an individual decides whether or not to participate. When an individual is considering joining a clinical trial, the research staff will provide informed consent documents that include details about the study. But informed consent is more than just signing a form. It is a continuous process, with the research team providing information throughout the course of the trial. Since joining a clinical trial is an important decision, people are encouraged to discuss all their questions and concerns with the research team before deciding whether to participate.

Clinical trials of experimental drugs proceed through four phases:

• In Phase I clinical trials, researchers test a new drug or treatment in a small group of people for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
• In Phase II clinical trials, the study drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.
• In Phase III studies, the study drug or treatment is given usually to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
• Phase IV studies are done after the drug or treatment has been marketed. These studies continue testing the study drug or treatment to collect information about its effect in various populations and any side effects associated with long-term use.

All clinical trials are based on a set of rules called a protocol. A protocol describes the criteria for participation; the schedule of tests, procedures, medications, and dosages; and the length of the study.