What are the potential risks and benefits of clinical trials?
How are participants protected?
What is informed consent?
Could participants receive a placebo?
What happens during a trial?
What happens after a trial?

What are the potential risks and benefits of clinical trials?

Potential benefits include

  • health care provided by leading physicians in the field of research
  • access to new drugs and interventions before they are widely available
  • close monitoring of volunteers' health care and any side effects
  • a more active role in personal health care
  • if the approach being studied is found to be helpful, volunteers may be among the first to benefit
  • an opportunity to make a valuable contribution to cancer research

Potential risks include

  • new drugs and procedures may have side effects or risks unknown to the doctors
  • new drugs and procedures may be ineffective, or less effective, than current approaches
  • even if a new approach has benefits, it may not work for everyone

How are participants protected?

The government has a system designed to protect human research subjects. Before a clinical trial can begin, the trial plan (also called a protocol) must be approved. During the trial, review committees make sure that the plan is being followed and participants are being protected.

Regulations require the researchers performing studies to thoroughly inform patients about a study's treatments and tests and their possible benefits and risks before a patient decides whether or not to participate in any study. This process is called informed consent.

What is informed consent?

Informed consent is a process by which volunteers learn the key facts about a clinical trial before they decide whether or not to participate. In addition to talking about these facts with the research doctor or nurse, they are included in a written consent form that can be taken home to read and discuss with others. The consent form includes details about:

  • the study approach
  • the intervention given in the trial
  • the possible risks and benefits
  • any tests required

Volunteers should not hesitate to ask questions until they have all the information they need. While informed consent begins before   a trial begins, participants should feel free to ask the health-care team any questions they have at any point. Informed consent continues throughout the study. Participants can change their minds and leave the study whenever they want, whether it is before the study starts or at any time during the study or follow-up period.

See A Guide to Understanding Informed Consent for additional information about this important process.

Could participants receive a placebo?

A placebo is an inactive substance or treatment that looks the same as, and is given the same way as, an active drug or treatment being tested in a clinical trial.

Many treatment trials are designed to compare a new treatment with a standard treatment, which is the best treatment currently known for a cancer based on results of past research. In these studies, patients are randomly assigned to one group or another. When no standard treatment exists for a specific disease, a study may compare a new treatment with a placebo. However, participants will be told about this possibility during informed consent, before they decide whether or not to take part in the study.

What happens during a trial?

Participants in a clinical trial will work with a research team. Team members may include doctors, nurses, social workers, dieticians, and other health care professionals. They will provide care, monitor participants' health carefully, and give specific instructions about the study.

Participating in a trial may mean that you might have more tests and doctor visits than you would if you weren't in the study. Team members also may continue to stay in contact with you after the trial ends. To make the trial results as reliable as possible, it is important for participants to follow the research team's instructions. That means having all doctor visits and tests, taking medicines on time, and completing logs or answering questionnaires.

What happens after a trial?

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 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 agent or intervention because it was unsafe or ineffective. When a phase III trial is completed, the researchers examine the data and decide whether the results have medical importance.

Results from clinical trials are often published in peer-reviewed scientific journals. Peer review is a process by which experts review the report before it is published to ensure that the analysis and conclusions are sound. If the results are particularly important, they may be featured in 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 the standard of medical practice.

Research team members can provide information as to whether or not 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:


The website of the National Cancer Institute (