National Institutes of Health (NIH) Institutes and Centers, including the NHLBI, support many types of clinical trials that contribute to medical knowledge and practice. Clinical trials can be described in a number of different ways, including by their purpose or by phase.
Clinical trials have different purposes. What that purpose is helps define the type of trial it is.
Researchers conduct clinical trials in a series of steps called phases. Each phase has a different purpose and helps researchers answer different questions.
As a participant in a clinical trial, you may work with a healthcare team, and you may need to go to a hospital or other location. Everything that happens throughout your experience follows a plan called a clinical trial protocol. Governing bodies called Institutional Review Boards (IRBs) approve protocols and are responsible for ensuring your safety. The research team will also operate by other national and international standards that protect you and help produce reliable study results. The NHLBI is one of many types of organizations that support clinical trials. Before you join a clinical trial, you will be told all about the study, what procedures you will be undergoing, how much time you will be spending on aspects of the study, and any other information you need to know. Once your questions have been answered and you are comfortable, you will be asked to give your consent to participate.
During a clinical trial, you may see doctors, nurses, social workers, and other healthcare providers who will monitor your health closely. You may have more tests and medical exams than you would if you were not taking part in a clinical trial. You may also be asked to do other tasks, such as keeping a log about your health or filling out forms about how you feel.
You may need to travel or stay in a hospital to take part in clinical trials. For example, the NIH Clinical Center in Bethesda, Maryland, runs clinical trials. It is the largest research hospital in the world. Many other clinical trials take place in medical centers and doctors’ offices around the country. If you decide that a trial is not for you, it is important to remember that you can withdraw at any time. Whether you participate or not will not affect your regular medical care.
Clinical trials follow a plan known as a protocol. The protocol is carefully designed to balance the potential benefits of a trial with the risks to participants. It also answers specific research questions. A protocol describes the following:
A clinical trial team is led by a principal investigator (PI). Members of the research team regularly monitor the participants’ health to determine the study’s safety and effectiveness.
There are different types of clinical trials and different trial designs. However, many clinical trials include standard design elements.
Randomization is the process by which participants are randomly assigned a treatment instead of being selected for one or the others. This is done to avoid bias when making assignments. The effects of each treatment are compared at specific points during a trial. If one treatment is found superior, the study is stopped so that all the volunteers receive the more beneficial treatment.
Blinded or masked studies are designed to prevent members of the research team and study participants from influencing the results. Blinding allows the collection of scientifically accurate data.
After a clinical trial is completed, the researchers carefully examine information collected during the study before making decisions about the meaning of the findings and about the need for further testing. After a phase I or II trial, the researchers decide whether to move on to the next phase or to stop testing the treatment or procedure because it was unsafe or not effective. When a phase III trial is completed, the researchers examine the information and decide whether the results have medical importance.
Results from clinical trials are often published in scientific journals in articles that have gone through peer review. Results that are particularly important may be featured in the news, and discussed at scientific meetings and by patient advocacy groups. Once a new approach has been proven safe and effective in a clinical trial, it may become a new standard of medical practice. In many cases, if you participated in a blinded or masked study, you will get information about the treatment you received
Ask the research team members if the study results have been or will be published. Published study results are also available by searching for the study's official name or Protocol ID number in the National Library of Medicine's PubMed® database.
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.
How much of your time is needed, discomfort you may feel, or risk involved depends on the clinical trial. While some studies require minimal amounts of time and effort, other studies 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.
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.
Research with patient volunteers also helps develop new knowledge. Depending on the stage of knowledge 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.
In the past, clinical trial volunteers often were 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 to the same medical approach. As a result, the 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, as 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 also can affect how safe a treatment is or how well it works.
Learn more about clinical trials for children at the NHLBI’s Children and Clinical Studies page.
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, and whether you have had certain treatments or 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 and keep them safe, and to help ensure that researchers can find the new information they need.
Clinical trials offer hope for many people, while giving researchers a chance to find treatments that could benefit patients in the future. Healthy volunteers say they take part to help others and contribute to moving science forward. People with an illness or disease may take part to help others, but also to have a chance to receive the newest treatment and get added care and attention from the clinical trial staff. Clinical trials may involve risk, as can routine medical care and the activities of daily living. When weighing the risks of clinical trials, consider the possible harms that could result from taking part in the study, the level of harm, and the chance of any harm occurring.
Clinical trials do come with some risks.
In clinical trials that compare a new product or therapy with another that already exists, researchers try to determine if the new one is as good, or better than, the existing one. In some studies, you may receive a placebo. Comparing a new product with a placebo can be the fastest and most reliable way to show the new product's effectiveness. However, placebos are not used if you would be put at risk—particularly in the study of treatments for serious illnesses—by not having effective therapy. You will be told if placebos are used in the study before entering a trial.
You can learn about the risks and benefits of any clinical trial and how your rights are protected before you agree to take part in the trial. A member of the research team will explain the study and answer any questions about the study. A member of the research team will also ask you to consider and sign an informed consent document, which will describe in detail the specific risks associated with a research protocol. Before deciding to participate, carefully consider risks and possible benefits. You can also talk with your doctor about specific clinical trials you are interested in.
See a list of questions to ask your doctor and the research staff.
If you are thinking about taking part in a clinical trial, you should feel free to ask any questions or bring up any issues concerning the trial at any time. The following suggestions may give you some ideas as you think about your own questions.
Possible benefits and risks
Participation and care
Protecting the safety of people who take part in clinical trials is a high priority for the NHLBI and its researchers. You also have rights to help protect your safety.
Each study has scientific oversight, including the following:
As a participant in a clinical trial, you have rights that help protect your safety. These rights include:
The NHLBI has a strong tradition of supporting clinical trials that have shaped medical practice around the world. These trials have improved the health of millions of people suffering from heart, lung, and blood disorders.
Based on input from a broad group of stakeholders and advisory groups, the NHLBI established a multi-pronged approach to making our clinical trials enterprise even stronger. This effort is called Optimize our Clinical Trials Enterprise.
The NHLBI's funding announcements will help lead investigators to more interpretable, timely, and useful results, which in turn will improve public health. We offer a variety of funding mechanisms tailored to planning and conducting clinical trials at all phases, including pilot studies. View funding information for clinical trials optimization.
The NHLBI leads or supports many studies aimed at preventing, diagnosing, and treating heart, lung, blood, and sleep disorders. Find NHLBI clinical trials that are currently enrolling participants.
After reading our Clinical Trials Health Topic, you may be interested in additional information found in the following resources.