Patient volunteers in clinical trials may be able to help make medical advances possible. Their commitment to improving our knowledge and understanding about various diseases and treatments is heroic. We are indebted to the thousands of volunteers who participate in clinical trials each year. Without them, no new medical treatments can be realized.

There are many reasons people volunteer for clinical trials.

People with an illness or disease may participate to possibly receive the newest investigational medication and also to possibly help researchers find better treatments for others in the future. Healthy volunteers say they participate to help others and to contribute to moving science forward.

Yet more trial participants are needed. Under-enrollment in trials is one of the greatest challenges clinical researchers face. It’s estimated that across all diseases, 80 percent of clinical trials finish late due to difficulties enrolling participants, and nearly one-third of trials fail to recruit a single subject and cannot ever begin.

Ultimately, choosing to participate in a clinical trial is a deeply personal decision for both patients and their support network of family, friends and caregivers. It’s important to gather as much information as possible to make it an informed decision.

Benefits and Risks of Participating in a Clinical Trial
Clinical trials that are well-designed and well-executed are the best approach for eligible participants to:

  • Play active roles in their own healthcare.
  • Gain access to new investigational medications before they are widely available.
  • Help others by contributing to medical research.

There are also risks to clinical trials:

  • There may be unpleasant, serious or even life-threatening side effects to treatment.
  • The treatment may not be effective for the participant.
  • The protocol may require more of their time and attention than would a non-protocol treatment, including trips to the study site, more treatments, hospital stays or complex dosage requirements.
What to Consider Before Participating in a Clinical Trial
You should know as much as possible about the clinical trial and feel comfortable asking the members of the healthcare team questions about it, the care expected while in a trial and the cost of the trial. These questions might be helpful to discuss with the healthcare team. Some of the answers to these questions will be found in the informed consent document.

All clinical trials have guidelines about who can participate. Using inclusion/exclusion criteria is an important principle of medical research that helps 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 such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions.

Before joining a clinical trial, a participant must qualify for the study. Some research studies seek participants with illnesses or conditions to be studied in the clinical trial, while others need healthy participants. It is important to note that inclusion and exclusion criteria are not used to reject people personally. Instead, the criteria are used to identify appropriate participants and keep them safe. The criteria help ensure that researchers will be able to answer the questions they plan to study.

The clinical trial process depends on the kind of trial being conducted. The clinical trial team includes doctors and nurses as well as social workers and other healthcare professionals. They check the health of the participant at the beginning of the trial, give specific instructions for participating in the trial, monitor the participant carefully during the trial, and stay in touch after the trial is completed.

Some clinical trials involve more tests and doctor visits than the participant would normally have for an illness or condition. For all types of trials, the participant works with a research team. Clinical trial participation is most successful when the protocol is carefully followed and there is frequent contact with the research staff.

The Informed Consent Process Protects Participants
Informed consent is the process in which researchers communicate with potential and enrolled participants about a clinical study. It provides the potential benefits as well as the risks to the patient. It informs the patients that participation in the trial is voluntary, and they may discontinue participation at any time.

The goal of the informed consent process is to protect participants. It begins when a potential participant first asks for information about a study and continues until the study ends.

Before you begin the screening process to determine eligibility for the clinical trial, the research team will provide you with details about the study and answer any questions so that you are thoroughly informed about the trial, its procedures and potential risks/benefits, use and potential disclosure of personal health information, and alternatives to trial participation, among other details. At this point, if you decide to participate, you will sign an Informed Consent Form showing that you have been given this information and understand it.

The Informed Consent Form will include information that tells you:

  • the fact that the study involves research of an unproven drug or device
  • the purpose of the research
  • how long the study will take
  • what will happen in the study and which parts of the study are experimental
  • possible risks or discomforts
  • possible benefits
  • other procedures or treatments that you might want to consider instead of the treatment being studied
  • that the FDA may look at study records, but the records will be kept secret
  • whether any medical treatments are available if you are hurt, what those treatments are, where they can be found, and who will pay for the treatment
  • the person to contact with questions about the study or your rights, or if you get hurt
  • that you can quit at any time

Volunteers can leave the study at any time, for any reason, even after they’ve signed the Informed Consent Form.

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Becoming knowledgeable and informed is a first step when considering participation in a clinical trial. These additional resources for patients and caregivers may help you. 

Discover some of the resources available for patients and caregivers. 


Merck-sponsored clinical trials in patients are registered on, a service of the U.S. National Institutes of Health. Information about ongoing clinical trials is also available online through the International Federation of Pharmaceutical Manufacturers & Associations (IFPMA), a global non-profit non-governmental organization representing the research-based pharmaceutical, biotech and vaccine sectors.

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