About Clinical Trials


Being in a clinical trial is different from being treated as a patient who is not participating in a clinical trial. If you choose to participate in a clinical trial you will become a research study participant. Trials are done because researchers want to answer scientific questions and to advance medical knowledge.

The answers obtained from clinical trials may offer benefits to future patients and to society. It is important to understand that as an individual research study participant, you may or may not benefit from participating in a trial.

A clinical trial can usually be categorized as falling into one of four stages or "phases."

​​ Phase IPhase I studies are designed to determine how the drug interacts with the human body, some of the side effects of increasing doses, and, occasionally, early evidence of effectiveness.

Usually, healthy participants are enrolled in Phase I studies; however, participants with the disease being studied may under certain circumstances be enrolled. The total number of participants included in Phase I studies varies with the drug, but is generally in the range of 20-80.
Phase IIIn Phase II studies, researchers administer the drug — at the doses and on the schedule found to be safe in Phase 1 trials — to participants with the disease or condition of interest. They also collect safety and effectiveness data, study short-term side effects and risks, and note additional information about the proper dose and dosing schedule.

Phase II studies typically involve control gr​oups, are closely monitored, and are usually conducted in groups of not more than several hundred participants.
Phase IIIPhase III studies are intended to gather the additional information about effectiveness and safety that is needed to evaluate the overall benefit/risk relationship of the drug. Researchers collect additional information about drug-related bad side effects, including the less common side effects.

Several hundred to several thousand participants may be enrolled. At the conclusion of a properly designed Phase III trial, the new drug will be found to be superior, equivalent, or inferior to the standard treatment — and will then be approved or rejected by the U.S. Food and Drug Administration (FDA).
Phase IVAfter the FDA has approved a drug, researchers gather additional information about the drug's risks, benefits, and best uses using data from with large-scale usage in real-life conditions.

These studies can also include trials of different doses or schedules of administration, at other stages of disease, cost studies, quality-of-life studies, or studies in the use of the drug over a longer period of time.

If you want more detailed information about what it means to be a research study participant in a clinical trial, the National Institutes of Health has prepared a page with answers to some commonly asked questions.

You may also have questions about the specific study you're considering participating in. If you need clarification about risks, benefits, or anything else related to your particular study be sure to ask the researcher in your initial discussion.​