Clinical Trials


A man talking to a woman in an office.

You wanna know more about clinical trials? You can find the answers to eleven frequently asked questions in our FAQ below.

Clinical trials are research studies conducted with people who volunteer to take part in testing how well new medical approaches work. Each study answers scientific questions and tries to find better ways to prevent, screen for, diagnose, or treat a disease.

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.

Trials can take place in a variety of locations, such as hospitals, universities, doctors' offices, or community clinics.

Research with people is conducted according to strict scientific and ethical principles. Every clinical trial has a protocol which acts like a "recipe" for conducting the trial. The protocol describes what will be done in the study, how it will be conducted, and why each part of the study is necessary. The same protocol is used by every doctor or research center taking part in the trial.


To ensure the safety of those in the study various approvals are required; these vary depending on the country but usually include a central review by a government department and also locally. The review ensures participants are treated humanely and ethically and whether the likely benefit of the treatment is worth its risk.

Each study's protocol has guidelines for who can or cannot participate in the study. These guidelines, called eligibility criteria, describe characteristics that must be shared by all participants. The criteria differ from study to study. They may include age, gender, medical history, and current health status. 
Enrolling participants with similar characteristics ensures that the results will be due to what is under study and not other factors. In this way, eligibility criteria help researchers achieve accurate and meaningful results. These criteria also make certain that people who could be made worse by participating in the study are not exposed to the risk.

Informed consent is a process by which people learn the important facts about a clinical trial to help them decide whether to participate. This information includes details about what is involved, such as the purpose of the study, the tests and other procedures used in the study, and the possible risks and benefits. In addition to talking with the doctor or nurse, people receive a written consent form explaining the study. People who agree to take part in the study are asked to sign the informed consent form. However, signing the form does not mean people must stay in the study. People can leave the study at any time - either before the study starts or at any time during the study or the follow-up period. The informed consent process continues throughout the study. If new benefits, risks, or side effects are discovered during the study, the researchers must inform the participants. They may be asked to sign new consent forms if they want to stay in the study.

Clinical trials take place in doctors' offices, medical centers, community hospitals and clinics. Clinical trials may include participants at one or two highly specialized centers, or they may involve hundreds of locations at the same time.

Clinical trials are usually conducted in a series of steps, called phases.

  • Preclinical trials are early experiments performed in the lab prior to being tested in humans. This early research helps to identify potential treatments that are unsafe or ineffective.
  • Phase I trials are the first step in testing a new approach in humans. In these studies, researchers evaluate what dose is safe, how a new agent should be given (by mouth, injected into a vein, or injected into the muscle, for example), and how often. Researchers watch closely for any harmful side effects. Phase I trials usually enroll a small number of patients and take place at only a few locations.
  • Phase II trials study the safety and effectiveness of an agent or intervention, and evaluate how it affects the human body. Phase II studies usually focus on a particular medical condition.
  • Phase III trials compare a new agent or intervention (or new use of a standard one) with the current standard therapy. Participants are randomly assigned to the standard group or the new group, usually by computer. This method, called randomization, helps to avoid bias and ensures that human choices or other factors do not affect the study's results. In most cases, studies move into Phase III testing only after they have shown promise in Phases I and II. Phase III trials may include hundreds of people across the country or globally.
  • Phase IV trials are conducted to further evaluate the long-term safety and effectiveness of a treatment. They usually take place after the treatment has been approved for standard use. Several hundred to several thousand people may take part in a Phase IV study. These studies are less common than Phase I, II, or III trials.

After a Phase I or II trial, the researchers decide whether to move on to the next phase, or stop testing the agent or intervention because it was not safe or effective. When a Phase III trial is completed, the researchers look at the data and decide whether the results have medical importance.
The results of clinical trials are often published in peer-reviewed, scientific journals and at company or other public websites like on the internet. Peer review is a process by which experts review the report before it is published to make sure the analysis and conclusions are sound. If the results are particularly important, they may be featured by the media and discussed at scientific meetings and by patient advocacy groups before they are published. Once a new approach has been proven safe and effective in a clinical trial, it may become standard practice. (Standard practice is a currently accepted and widely used approach.)

The benefits of participating in a clinical trial include the following:

  • Participants have access to promising new approaches that are often not available outside the clinical trial setting.
  • The approach being studied may be more effective than the standard approach.
  • Participants receive regular and careful medical attention from a research team that includes doctors and other health professionals.
  • Participants may be the first to benefit from the new method under study.
  • Results from the study may help others in the future.

The possible risks of participating in a clinical trial include the following:

  • New drugs or procedures under study are not always better than the standard care to which they are being compared.
  • New treatments may have side effects or risks that doctors do not expect or that are worse than standard care.
  • Participants in randomized trials will not be able to choose the approach they receive.
  • Depending on countries and health insurance systems, health insurance and managed care providers may not cover all patient care costs in a study.
  • Participants may be required to make more visits to the doctor than they would if they were not in the clinical trial.

It is important for people to ask questions before deciding to enter a clinical trial. Some questions people might want to ask their doctor or nurse are below.

The trial

  • What is the purpose of the trial?
  • Why do the researchers think the approach being tested may be effective? Has it been tested before?
  • Who is sponsoring the trial?
  • Who has reviewed and approved the trial?
  • What are the medical credentials and experience of the researchers and other study personnel?
  • How are the trial results and safety of participants being monitored?
  • How long will the trial last?
  • How will the results be shared?


Possible risks and benefits

  • What are the possible short-term benefits?
  • What are the possible long-term benefits?
  • What are the short-term risks, such as side effects?
  • What are the possible long-term risks?
  • What other treatment options are available?
  • How do the possible risks and benefits of the trial compare with those of other options?


Participation and care

  • What kinds of treatment, medical tests, or procedures will the participants have during the study? How often will they receive the treatments, tests, or procedures?
  • Will treatments, tests, or procedures be painful? If so, how can the pain be controlled?
  • How do the tests in the study compare with what people might receive outside the study?
  • Will participants be able to take their regular medications while in the clinical trial?
  • Where will the participants receive their medical care? Will they be in a hospital? If so, for how long?
  • Who will be in charge of the participants' care? Will they be able to see their own doctors?
  • How long will participants need to stay in the study? Will there be follow-up visits after the study?


Personal issues

  • How could being in the study affect the participants' daily lives?
  • What support is available for participants and their families?
  • Can potential participants talk with people already enrolled in the study?

Cost issues*

  • Will participants have to pay for any treatment, tests, or other charges?
  • If so, what will the approximate charges be?
  • Will my health care insurance provider have to take over parts of the cost?
  • Who can help me if I require more information regarding financial issues?

* Cost issues can depend on individual regulations in countries and health care insurance providers.