Placebos in Cancer Clinical Trials

Approved by the Cancer.Net Editorial Board, 10/2022

A placebo is a drug or treatment that is not active. Placebos are used in some clinical trials, which are research studies done with volunteers.

Researchers may use placebos in cancer clinical trials to learn if the new drug or treatment works better than a substance that does not have an active drug in it (the placebo). A placebo is sometimes called a "sugar pill." In general, the placebo usually looks like the drug or other treatment being studied, but it has no active ingredients.

People who participate in cancer clinical trials may receive a placebo, which is not considered to have any benefit. Participants will be told whether they study they join is using a placebo. It is important to know that whenever a placebo is used in a cancer clinical trial, people who receive the placebo will also receive the standard treatment for the specific cancer as well.

Are placebos used in cancer clinical trials?

Placebos are sometimes used in cancer clinical trials. When a placebo is used, the person will also receive the the standard treatment for their specific cancer.

When researchers do use a placebo, they must:

  • Tell volunteers that they have a chance of getting a placebo

  • Tell them if they will receive an experimental treatment at some point in the clinical trial, if not right away

Cancer clinical trials can be designed so people have less chance of getting a placebo or the placebo amount is limited. For example, you may be assigned to the placebo group. But if your cancer gets worse, researchers will switch you to the study drug or treatment.

Why are placebos used more now than in the past?

In the past, it was very rare to use a placebo in a cancer clinical trial. This was because most chemotherapy had obvious effects, such as visibly shrinking the tumor or causing side effects that only an active drug could produce. This made it fairly easy to tell if the new drug or treatment had an effect.

Today, many cancer treatments have less obvious effects. For example, a targeted therapy may slow down tumor growth, but not shrink the tumor as much. Or the side effects might be very similar to those most people with cancer have, such as feeling tired. So researchers need to compare the new drug or treatment to something. Using a placebo can help them learn what effect the new treatment really has.

When placebos may be used in cancer clinical trials

It can be helpful to use a placebo when researchers first test a new drug. They want to learn if it actually treats the cancer and what effects it causes. The volunteers may be people who have already received all the treatments known to be effective. They may receive a placebo, but they may also receive the study drug or treatment.

Placebos may be appropriate in with diseases or treatments when:

  • Comparing it to a new treatment helps researchers learn if the new treatment works even better

  • The type of cancer being studied tends to get better and then worse, or signs of disease go away at times (called remission)

  • The known treatments do not work well or cause serious side effects

  • There is no known effective treatment

You should not be in a clinical trial where you could get a placebo instead of active treatment if:

  • Your health is worse than most other volunteers' health
  • You are more likely to have serious side effects or severe discomfort than others

Everyone in the clinical trial should receive care to keep them as comfortable as possible and relieve side effects. This type of care is called supportive care or palliative care.

Why do we ever need cancer clinical trials with placebos?

Clinical trials are the best way to develop new drugs and other treatments for cancer. Until this type of research proves the new treatment is safe and effective, it cannot be made available to the public in the United States. Comparing the new treatment to a placebo is sometimes the best way to prove safety and effectiveness.

When should a placebo not be used?

A placebo should not be used instead of a known treatment or one that cures the cancer. If researchers want to test a new treatment when a known treatment is available, the clinical trial can include:

  • The new treatment plus the treatment known to work, or

  • The placebo plus the treatment known to work.

This way, all the volunteers get at least one treatment that is known to work or cure the cancer. No one should receive an unproven treatment plus a placebo if an effective treatment also exists.

Questions to ask the health care team

  • What is the purpose of this clinical trial?

  • How is the treatment different from the regular treatment or standard care?

  • Does this clinical trial include the use of a placebo? What does this mean?

  • What are my chances of receiving a placebo? What will that mean for my care? Is it possible that I could lose out on more effective treatments?

  • Could I be switched to the standard treatment or study treatment during the clinical trial? If so, why and when?

  • What other treatment options are available, including the standard treatments and other clinical trials?

  • What are the risks of this clinical trial for me? What are the benefits?

  • How do the risks and benefits of this clinical trial compare to the risks and benefits of standard treatment?

  • How do the risks and benefits of this clinical trial compare with other clinical trials I could join?

Related Resources

Questions to Ask About Clinical Trials

The Importance of Clinical Trials in Treating People with Cancer

Patient Safety in Clinical Trials

When Joining a Cancer Clinical Trial Is Your Last Treatment Option

More Information

The Center for Information & Study on Clinical Research Participation: Should I Participate? (PDF)

National Cancer Institute: Questions to Ask Your Doctor About Treatment Clinical Trials