For Patients

Choosing to participate in a clinical trial is an important personal decision. The following frequently asked questions provide detailed information about clinical trials. In addition, it is often helpful to talk to a physician, family members, or friends about deciding to join a trial. After identifying some trial options, the next step is to contact the study research staff and ask questions about specific trials.

A clinical trial is a health-related or biomedical research study in human beings. Clinical trials (also called medical research and research studies) are used to determine whether new drugs or treatments are both safe and effective. Carefully conducted clinical trials are important to find treatments and therapies for various diseases and health conditions.

Who sponsors clinical trials?

Clinical trials are sponsored or funded by a variety of organizations or individuals such as physicians, medical institutions, foundations, voluntary groups, and pharmaceutical companies, in addition to federal agencies such as the National Institutes of Health (NIH), the Department of Defense (DOD), and the Department of Veterans' Affairs (VA). Trials can take place in a variety of locations, such as hospitals, universities, doctors' offices, or community clinics.

What are the different types of clinical trials?

Treatment trials test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy. 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, vitamins, vaccines, minerals, or lifestyle changes. Screening trials test the best way to detect certain diseases or health conditions. Quality of life trials (or supportive care trials) explore ways to improve comfort and the quality of life for individuals with a chronic illness.

What are the phases of clinical trials?

Clinical trials are conducted in phases usually numbered I - IV. The trials at each phase have a different purpose and help scientists answer different questions: In Phase I trials, researchers test a new drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. In Phase II trials, the study drug or treatment is given to a larger group of people (100-300) to see if it is effective and to further evaluate its safety. In Phase III trials, the study drug or treatment is given to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it with commonly used treatments, and collect information that will allow the drug or treatment to be used safely. In Phase IV trials, post-marketing studies delineate additional information including the drug's risks, benefits, and optimal use.

Participants in clinical trials can play a more active role in their own health care, gain access to experimental therapeutics before they are widely available, and help others by contributing to medical research. 

Why should I participate in a clinical trial?

Participants in clinical trials gain access to experimental therapies before they are widely available, and help others by contributing to medical research.

People participate in research for many reasons. Healthy people frequently participate in research studies to contribute to medical science and care for others. If you have a specific illness, enrolling in a clinical trial can offer access to new, experimental approaches to treatment that are often unavailable outside of a research setting.

What are the benefits and risks of participating in a clinical trial?

Below are some potential benefits of participation in research:

  • If you have a disease or condition that cannot be treated with an existing drug or therapy, study participation may provide you with access to promising new approaches to treatment not available otherwise.
  • If you are debilitated in some way, you may have the opportunity to test a therapy that might improve your quality of life.
  • If you have a specific medical problem for which you are experiencing difficulty finding good care, you may find access to improved care within a clinical trial, since the study doctors involved in the research focus directly on the disease or condition being investigated.
  • You may be altruistic; that is, you may have an interest in helping others in general, or helping those with a specific disease or condition. The results from clinical trials conducted today may help patients in the future.


There are potential risks to clinical trial participation:

  • There may be unpleasant, serious, or even life-threatening side effects from the experimental treatment or therapy.
  • The treatment may not be effective for the participant.
  • The protocol may require more of the participant’s time and attention than would a non-protocol treatment, requiring trips to the study site, more treatments, hospital stays, or complex dosage requirements.

Who can participate?

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. The criteria help ensure that researchers will be able to answer the questions they plan to study.

Although there is an important distinction between medical care and research, the ethical and legal codes that govern medical practice also apply to clinical trials. In addition, most clinical research is federally regulated with built-in safeguards to protect the participants. 

The ethical and legal codes that govern medical practice also apply to clinical trials. In addition, most clinical research is federally regulated with built-in safeguards to protect the participants. The trial follows a carefully controlled protocol, a study plan that details what researchers will do in the study. As a clinical trial progresses, researchers report the results of the trial at scientific meetings, to medical journals, and to various government agencies. Individual participants' names will remain confidential and will not be mentioned in these reports.


Every clinical trial in the U.S. must be approved and monitored by an institutional review board (IRB) to make sure the risks are as low as possible and are worth any potential benefits. An IRB is an independent committee of physicians, statisticians, community advocates, and others that ensures that a clinical trial is ethical and the rights of study participants are protected. All institutions that conduct or support biomedical research involving people must, by federal regulation, have an IRB that initially approves and periodically reviews the research.

Leaving a trial

A participant can leave a clinical trial, at any time and for any reason. When withdrawing from the trial, the participant should let the research team know about it, and the reasons for leaving the study.

Informed consent

Informed consent is the process of learning the key facts about a clinical trial before deciding whether or not to participate. It is also a continuing process throughout the study to provide information for participants. To help someone decide whether or not to participate, the doctors and nurses involved in the trial explain the details of the study. If the participant's native language is not English, translation assistance can be provided. Then the research team provides an informed consent document that includes details about the study, such as its purpose, duration, required procedures, and key contacts. Risks and potential benefits are explained in the informed consent document. The participant then decides whether or not to enroll in the study. If an individual chooses to participate, he or she is asked to sign the informed consent document. Informed consent is not a contract, and the participant may withdraw from the study at any time.

The clinical trial process depends on the kind of trial being conducted. 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.

Before the clinical trial

You should know as much as possible about the clinical trial and feel comfortable asking the members of the research team questions about it, such as the care you can expect while participating in a trial, and whether there are any costs associated with participation. Prepare for the meeting with the research coordinator or doctor by planning ahead and writing down possible questions to ask. Bring a friend or relative for support and to hear the responses to the questions, and feel free to use a tape recorder to record the discussion to replay later.

The following questions might be helpful for the participant to discuss with the healthcare team:

  • What is the purpose of the study?
  • Who is going to be in the study?
  • Why do researchers believe the new treatment being tested may be effective? Has it been tested before?
  • What kinds of tests and treatments are involved?
  • How do the possible risks, side effects, and benefits in the study compare with my current treatment?
  • How might this trial affect my daily life?
  • How long will the trial last?
  • Will hospitalization be required?
  • Who will pay for the treatment?
  • Will I be reimbursed for other expenses?
  • What type of long-term follow-up care is part of this study?
  • How will I know that the treatment is working?
  • Will results of the trial be provided to me?
  • Who will be in charge of my study-related care?