Clinical Trials
Clinical Trials

Clinical Trials How Clinical Trials Work

What are clinical trials?

Clinical trials are medical studies that involve people like you. They help find new ways to prevent, detect, or treat diseases that are safe and effective. The National Heart, Lung, and Blood Institute (NHLBI) leads and supports many studies aimed at preventing, diagnosing, and treating heart, lung, blood, and sleep disorders.

Clinical trials are an important part of the research spectrum. The idea for a clinical trial often starts in the lab. After researchers test new treatments or procedures in the lab and in animals, the most promising treatments are moved into clinical trials. As studies about new treatments move through a series of steps called phases, researchers learn more information about the treatment, its risks, and its effectiveness.

Each clinical trial has criteria describing who can join. Children as well as adults, patients and healthy volunteers, and people of a diverse range of ethnic and racial backgrounds can and are encouraged to participate in clinical trials.

Clinical trials follow a protocol, a carefully designed plan to safeguard your health and answer specific research questions. The protocol describes what you will be doing and what you can expect from the research team. It is important to understand the risks and benefits of participation before joining. You also have rights and protections as a participant in clinical trials.

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.

Purpose of clinical trials

Clinical trials have different purposes. What that purpose is helps define the type of trial it is.

  • Behavioral trials evaluate or compare ways to promote behavioral changes designed to improve health.
  • Diagnostic trials study or compare tests or procedures for diagnosing a particular disease or condition.
  • Prevention trials look for better ways to prevent a disease in people who have never had the disease or to prevent the disease from returning. Approaches may include medicines, vaccines, or lifestyle changes.
  • Quality-of-life trials, or supportive care trials, explore and measure ways to improve the comfort and quality of life for people with conditions or illnesses.
  • Screening trials test new ways for detecting diseases or health conditions.
  • Treatment trials test new treatments, new combinations of medicines, or new approaches to surgery or radiation therapy.

Clinical trial phases

Researchers conduct clinical trials in a series of steps called phases. Each phase has a different purpose and helps researchers answer different questions.

  • Phase I trials: Researchers test a medicine or other treatment in a small group of people for the first time. The purpose is to learn about the best dosage for a medicine or other treatment and to learn about the safety and side effects.
  • Phase II trials: Researchers study the new medicine or treatment in a larger group of people to determine its effectiveness and to further study its safety.
  • Phase III trials: Researchers give the new medicine or treatment to an even larger group of participants to confirm its effectiveness, monitor side effects, compare it with standard or similar treatments or a placebo , and collect information that will allow the new medicine or treatment to be used safely.
  • Phase IV trials: After the U.S. Food and Drug Administration (FDA) approves a medicine or treatment and it is made available to the public, researchers track its safety in the general population, seeking more information about the medicine or treatment’s benefits and optimal use.

Clinical trial experience

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 will not affect your regular medical care.

Clinical trial protocols

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:

  • Details about tests, procedures, and treatments
  • Eligibility requirements
  • Expected duration, or how long the study will last
  • Goals of the study
  • Information to be gathered
  • Protections against risks to participants

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.

Clinical trial designs

There are different types of clinical trials and different trial designs. However, many clinical trials include standard design elements.

  • 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.
    • In single-blind (single-masked) studies, you are not told what you are being given, but the research team knows.
    • In double-blind studies, neither you nor the research team are told what you are given; only the pharmacist knows. Members of the research team are not told which participants are receiving which treatment, in order to reduce bias. If medically necessary, however, it is always possible to find out which treatment you are receiving.
  • Randomization is the process by which participants are randomly assigned a treatment instead of being selected for one or the other. 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.

When the study is finished

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.

Participate in an NHLBI clinical trial

Search our list of research studies by topic, location, and age to see whether you or someone you know is eligible to join.

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