A Guide to Understanding Clinical Trials

woman working in lab

Clinical trials are scientific studies using human volunteers that determine the effectiveness, safety and tolerability of an intervention. The people who volunteer are told about the possible risks before starting the trial. Before a clinical trial can begin for a treatment, medication or device, it must show promising results in laboratory or animal tests.

Below are some common questions about clinical trials:

What happens during a clinical trial?

At the beginning of a clinical trial, a team of doctors, nurses, social workers and other health professionals checks the health of the proposed participants, identifies those that are eligible for the trial, and gives specific instructions for using the treatment, medication or device throughout the trial. Participants sign an informed consent prior to enrollment. Informed consent is the process of providing you with key information about the clinical trial before you decide to enroll. The team monitors the participants as the trial progresses and stay in touch for a week or two after the trial is completed. All clinical trials follow a detailed plan, called a protocol, which includes information on the length of the study and what information will be gathered.

Are clinical trials safe?

For the most part, yes. However, sometimes clinical trials are for investigational medications intended for people with a certain condition. In those cases, there may be more risks involved. The participant will always be advised of the potential risks and benefits involved in a trial in the informed consent document. All U.S. clinical trials must be approved and monitored by an Institutional Review Board (IRB) to ensure they are ethical and study participants’ rights are protected.

Who can participate in a clinical trial?

All clinical trial protocols include definitions of who is eligible to participate. Criteria may include age, gender, the type and stage of a disease, previous treatment history and other medical conditions. Some participants may be healthy volunteers, who serve as control groups.

Why participate in a clinical trial?

Your participation may help others by contributing to medical research. You also will have access new research treatments before they are widely available.

Do I have to stay in a hospital or leave my home for a clinical trial?

Participants are generally asked to come in for regular office visits at an accessible clinical trial site, which may be a doctor’s office, university medical center or community hospital or clinic. Some trials may involve occasional overnight hospital stays or require more doctor visits than would be normal for an illness or condition. Many trials involve a physical examination or medical history review prior to enrollment. A description of what’s expected of the participant should be made available before signing the informed consent document.

What kind of paperwork or legal agreements do I have to sign?

A member of the clinical trial research team will explain the risks and potential benefits. This information is also provided in an informed consent document, which the participant is required to sign before taking part in the trial. According to the FDA(link opens in new window), minimum required elements of an informed consent include the following:

Purpose of research
Foreseeable risks
Potential benefits
Disclosure of alternative procedures
Confidentiality
Course of action if more than minimal risk involved
Who to contact
Participation is voluntary

Can you quit after a clinical trial starts?

Entering a clinical trial is voluntary. If you start a study, you may stop at any time and you don’t need to give a reason.

How long do clinical trials typically last?

They vary greatly. Some last just a few days while others take years.

If I decide to take part in a clinical trial, what should I do to prepare?

You should learn as much about the trial as possible before signing the informed consent document. Helpful questions to ask the trial directors include:

What is the purpose of the study?
Why do researchers believe the experimental treatment being tested may be effective? Has it been tested before?
Who has reviewed and approved the study?
What are the possible risks, side effects and benefits of the study treatment?
What other options do people with my disease have?
How might this trial affect my daily life?
How long will the trial last?
What will be my responsibilities if I participate?
What kinds of tests and experimental treatments are involved?
Will they hurt, and if so, for how long?
Will I be able to take my regular medications while in the clinical trial?
Will hospitalization be required?
Who will pay for the experimental treatment, or is sponsoring the trial?
Will I be reimbursed for other expenses such as travel or child-care costs?
Who can help answer questions from my insurance company or health plan?
What type of long-term follow-up care is part of this study?
How will I know that the experimental treatment is working? Will results of the trials be provided to me?
Who will be in charge of my care?

Where can I find understandable definitions of some of the scientific terms used during a clinical trial?

The National Institutes of Health Clinical Trials Glossary(link opens in new window) lists more than 80 terms commonly used in clinical trials.

Where can I get more detailed information about clinical trials?

Helpful informational sources include:

How can I be sure a clinical trial is legitimate?

The sponsor or research coordinator should be able to answer all of your questions, such as whether the trial protocol is approved and will be monitored by an IRB, what is the purpose of the trial, what are the possible risks and how long the trial is expected to last.

Another resource is the National Institutes of Health Clinical Trial Registry at http://clinicaltrials.gov(link opens in new window). This site lists more than 200,000 trials in at least 190 countries. You can search for a trial using criteria such as condition or disease treated, medication or therapy used, or site country. Each entry includes a trial description, sponsors, purpose, estimated completion date, eligibility criteria and contact information.

The World Health Organization International Clinical Trials Registry Platform(link opens in new window) provides similar background information about trials across the worldwide.

What are the different types of clinical trials?

There are several kinds of trials, each with a different purpose:

Behavioral trials look at ways to examine how behavior changes can improve health and outcomes.
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.
Diagnostic trials evaluate tests or procedures for diagnosing a disease or condition.
Screening trials evaluate methods of detecting a disease or health condition.
Quality of life trials (or supportive care trials) evaluate methods of improving the comfort and quality of life of patients with chronic illness.

Are there different phases of clinical trials?

To be approved by the U.S. Food and Drug Administration, an experimental drug or treatment has to pass through several phases of clinical trials.

Phase I trials test an experimental drug or treatment in a small group of people (20-80) for the first time to evaluate its safety and identify side effects.
Phase II trials test the experimental drug or treatment in a larger group of people (100-300) to determine its effectiveness and continue evaluating safety.
Phase III trials test the experimental drug or treatment in a large group of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it with standard or equivalent treatments and continue evaluating safety.
Phase IV trials track additional information about an experimental drug or treatment's safety and optimal use after it has been approved by the FDA and made available to the public.

Who sponsors clinical trials?

Clinical trials can be sponsored by 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, the Department of Defense and the Department of Veterans Affairs.

Last Reviewed: Mar 2, 2021