Glossary of common clinical trial terms
Clinical trial research often includes terms that may not be familiar to you. For definitions of commonly used terms, visit our glossary.
A clinical trial is a research study designed to learn how our bodies respond to medicines or other treatments.
Who can take part in a clinical trial depends on the research question the trial is trying to answer (what the trial is being done for). Some trials recruit patients with a disease or other health condition that the clinical trial is studying. Other trials enroll healthy volunteers, which means you do not have a specific disease or health condition.
Ideas for clinical trials usually come from researchers. Researchers first test new investigational treatments in a lab. The treatments with the most promising results are moved into clinical trials to see if they are safe and work well for people.
Each clinical trial has a primary purpose – the main reason it’s being done.
- Treatment trials test new investigational treatments, new combinations of 2 or more drugs, or new uses for existing treatments
- 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 trials may include medicines, vitamins, vaccines, minerals such as calcium, or healthy life changes
- Diagnostic trials are done to find better tests or procedures for diagnosing a disease or condition
- Screening trials test the best way to find certain diseases or health conditions
- Quality of life trials (or supportive care trials) look at ways to improve comfort and the quality of life for people with a chronic (long-lasting) illness
Clinical trials may be paid for (sponsored) by different people or organizations, such as:
- Doctors
- Medical institutions
- Voluntary groups, such as charities or foundations
- Pharmaceutical companies
- Government agencies, such as the National Institutes of Health (NIH), the Department of Defense (DOD), or the Department of Veterans Affairs (VA)
Clinical trials may take place in:
- Hospitals
- Universities
- Doctors’ offices
- Community clinics
In many clinical trials, one group of participants will get the trial drug or investigational treatment being tested, while a second group, the control group, gets either an existing (standard) treatment or a placebo (a look-alike substance that does not contain an active drug or treatment). This is done to see how well the trial drug or investigational treatment works compared to the existing treatment or a placebo.
Side effects are any effects of a medicine, treatment, or intervention other than the main intended effect, and could be good, bad, or neutral. Investigational treatments must be tested for side effects that happen right away or after a longer time.
Adverse events (also called adverse effects) are medical problems that happen or worsen during a clinical trial. Adverse events may or may not be caused by the treatment a person took.
Before a clinical trial can start, it must be approved by an Institutional Review Board (IRB) to make sure the risks are as low as possible and are worth any possible benefits. An IRB is a committee of doctors, data experts, community advocates, and others who help ensure that a trial is done in an ethical way and the rights of participants are protected.
Each trial follows a carefully controlled plan (protocol) that explains what researchers will do during the trial. During the trial, researchers report the results to the trial’s IRB, to medical journals, and to government agencies. If problems such as severe side effects happen during a trial, it may be stopped or paused to protect participants.
Yes. Most trials study treatments related to an illness or health condition, but do not provide care for other conditions. Your doctor can also work with the trial team to make sure that other medicines you take do not affect the trial treatment.
Yes. You can leave a clinical trial at any time. If you decide to leave a trial, talk to the trial team first. The trial team may also ask about your reasons for leaving the trial.
If you don’t qualify for a clinical trial because of your age, health conditions, or other factors, but your doctors believe you would benefit from the trial treatment, sometimes you may be able to get the treatment through “expanded access.” Expanded access may be used to provide access to an investigational treatment for people with a life-threatening or serious disease for which there is no good existing treatment.
Federal agencies may approve expanded access for a trial treatment if:
- Researchers are actively studying the trial treatment in well-controlled clinical trials, or if all trials have been completed
- There is evidence that the trial treatment may work well to treat certain patients
- The benefits of the trial treatment outweigh the possible risks
Learn more about expanded access for specific treatments at: ClinicalTrials.gov
- Write down possible questions to ask
- Ask a friend or relative to come along for support and to hear answers to your questions
- Be prepared to record your meeting with your phone or other recording device so you can review it at home, if needed. You may need to ask the doctor for permission.
You can learn more about clinical trials, look up results from past trials, and find current trials at: ClinicalTrials.gov
