Clinical Trials
Clinical Trials

Clinical Trials Who Can Participate

Many different types of people take part in clinical trials. Some studies include healthy volunteers, while other studies include patient volunteers. Some studies include both healthy and patient volunteers . In addition, the NHLBI is committed to supporting clinical trials with diverse participants. This includes studies specific to children’s needs. Eligibility criteria determine who can participate in a clinical trial. Learn more about the many studies the NHLBI supports and their eligibility criteria.

How much of your time is needed, the discomfort you may feel, and the risk involved depend on the clinical trial. Although some studies require minimal amounts of time and effort, others may require a major commitment of your time and effort and may involve some discomfort. The clinical trial may also carry some risk. The informed consent process for volunteers includes a detailed discussion of what you will be asked to do as part of the study and any possible risks. Watch this video to learn more about participating in clinical research trials.

Healthy volunteers

Clinical trials with healthy volunteers are designed to develop new knowledge, not to provide direct benefit to those taking part. Researchers take measurements and make observations. Researchers may use the data to compare patient volunteers and healthy volunteers.

Patient volunteers

Research with patient volunteers also helps develop new knowledge. Depending on how much is known about the disease or condition, these procedures may or may not benefit the patient volunteer.

Patients may volunteer for studies similar to those in which healthy volunteers take part.

Diverse volunteers

In the past, clinical trial volunteers were often white men. Researchers assumed that study results were valid for other populations as well. Today, researchers realize that women and people from different racial and ethnic groups sometimes respond differently than white men do to the same medical approach. As a result, NIH and the NHLBI are committed to supporting clinical trials that include both men and women as well as racially and ethnically diverse populations.


Children need clinical trials that focus on them, because medical treatments and approaches often differ for children. For example, children may need lower doses of certain medicines or smaller medical devices. A child’s stage of development can also affect how safe a treatment is or how well it works.

Learn more about clinical trials for children at NHLBI’s Children and Clinical Studies page.

Eligibility criteria

A clinical trial's protocol describes who is eligible to take part in the research. Each study must include only people who meet the requirements for that study. These are the study’s eligibility criteria.

Eligibility criteria are different for each trial. They include whether you are a healthy or patient volunteer. They also include factors such as your age and sex, the type and stage of disease, whether you have had certain treatments, and whether you have other health problems.

The criteria ensure that new approaches are tested on similar groups of people. This makes it clear to whom a clinical trial’s results apply. Eligibility criteria are not used to reject people personally. Instead, the criteria are used to identify appropriate participants, keep them safe, and help ensure that researchers can find the new information they need.

Participate in an NHLBI clinical trial

Search our list of research studies by topic, location, and age to see whether you or someone you know is eligible to join.

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