Clinical Trial Basics

A clinical trial is a biomedical or health-related research study on human subjects that follows a pre-defined protocol or plan.

There are different types of clinical trials:

  1. Treatment trials test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
  2. Prevention trials look for better ways to prevent disease in people who have never had the disease or to prevent a disease from returning. These approaches may include medicines, vaccines, vitamins, minerals, or lifestyle changes.
  3. Diagnostic trials are conducted to find better tests or procedures for diagnosing a particular disease or condition.
  4. Screening trials test the best way to detect certain diseases or health conditions.
  5. Quality of Life trials (or supportive care trials) explore ways to improve comfort and the quality of life for individuals with a chronic illness.

Participation in a clinical trial is voluntary, and the volunteer does not have to be sick to join a study; many studies include people who don’t have a certain condition, as well as those who have it.

The research plan is carefully explained to those who volunteer before they agree to participate.

All clinical trials have guidelines about who can participate, using criteria that help to produce reliable results. The factors that allow someone to participate in a clinical trial are called “inclusion criteria” and those that disallow someone from participating are called “exclusion criteria.” These criteria are based on factors such as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions.

It is important to note that inclusion and exclusion criteria are not used to reject people for personal reasons. Instead, the criteria are used to identify appropriate participants and keep them safe. The criteria help to ensure that researchers will be able to answer the questions they plan to study.

For more information on clinical trials, visit, a service of the National Institutes of Health.

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