What is a Clinical Trial?

Clinical trial

A clinical trial is a research study designed to test the safety and/or effectiveness of drugs, devices, treatments, or preventive measures in humans. Clinical trials can be divided into three categories or "phases."

Phase I

Phase I trials are the first experiments using an investigational new drug in humans. Normally, healthy participants are enrolled in Phase I studies; however, participants with the disease being studied may, under certain circumstances, be enrolled into the trial. Phase I studies are designed to determine how the drug is broken down in the human body and how it interacts with the human body. Phase I studies reveal some of the side effects associated with increasing doses. When possible, some Phase I studies provide early evidence of effectiveness. Researchers use information from Phase I studies to design Phase II studies. The total number of participants included in Phase I studies varies with the drug, but is generally a small number of participants or a few dozen.

Phase II

Phase II trials continue to test the safety of the drug, and begin to evaluate how well the new drug works. Researchers collect additional safety and effectiveness information, study short-term side effects and risks, and collect additional information about the proper dose and dosing schedule. Phase II studies are closely monitored and typically involve control groups.

Phase III

Phase III trials are done after Phase I and Phase II studies have shown some evidence of effectiveness. They are longer-term research studies and are intended to gather the additional information about effectiveness and safety that is needed to evaluate the overall benefit/risk relationship of the drug. At the end of most Phase III trials the new drug will be found to be inferior, equal or superior to the standard treatment.