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Research Center

What is a Clinical Trial?

Clinical trials are a particular kind of clinical research: research involving people. They are considered only when they are shown to be safe and effective through basic science research. The term clinical trial emphasizes that the research is in a testing or trial stage before it can be approved for regular medical care. Clinical trials answer questions that can only be answered in research with people before a discovery can become a part of regular medical care.

Each clinical trial is very carefully planned to protect study participants and test effectiveness. Every trial must meet specific standards and be approved by the researcher's Institutional Review Board (IRB). The approved plan protects people who take part in the trial and describes how everything will happen to make sure the results are accurate and consistent.

Clinical Trial Phases

In addition to approved plans, clinical trials are conducted in 4 separate steps called "phases." Each phase has specific requirements and each one builds on the next. New drugs, devices and surgeries are required to go through all 4 phases to be approved for general use. Each phase of a clinical trial has a different purpose and helps scientists answer different questions.

In Phase I trials, researchers test an experimental drug or treatment in a small group of healthy people (20-40) to make sure it is safe, to find a safe dose, and learn about any side effects. In some circumstances, such as treatments for a serious condition, people with the condition will participate. A treatment or device can only be offered in Phase 1 trials after a lot of testing has already been done in laboratories and on animals (basic science research). Once the safety of the treatment or device has been confirmed, Phase II trials can begin.

In Phase II trials, studies can begin after the safety of the treatment or device has been confirmed in the Phase I trial. The treatment or device is given to a larger group of people (40-300) who actually have the disease or condition it is meant to treat. Phase II trials test how well a treatment or device works, and further test how safe it is. Once the treatment or device shows that it works and has no serious side effect, it can go to Phase III trials.

In Phase III trials, the treatment or device is given to even larger groups of people (1,000-3,000) to see how well it works and to compare it to treatments or devices already in common use. Researchers continue to monitor any side effects. After successful completion of Phase III trials, all the information is reviewed by the Food and Drug Administration (FDA) and if approved, the treatment or device can be sold for use in the general population.

In Phase IV trials, further studies may begin after the FDA has approved a treatment or device and it is being used in regular medical care. Researchers continue to monitor the treatment or device for things like side effects, complications, and general effectiveness value in new patient populations.

Clinical Trial Categories

There are several categories of clinical trials. Each of these categories contributes different kinds of information about health and disease as seen below:

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Last Reviewed: May 15, 2011

Susan   Wentz, MD, MS Susan Wentz, MD, MS
Director, Area Health Education Center
School of Medicine
Case Western Reserve University