You might know the term “placebo,”even if you’re not entirely sure what it is. In clinical trials, a placebo is an inactive substance or treatment that looks the same and is given the same way as an active drug or other treatment being studied. Placebos are generally used as a “control” to gauge how effective the active treatment is.
The fact that a placebo is an inactive substance that has no impact on health can be a frightening concept when you participate in a trial, hoping it will help treat cancer. “Using a placebo in a trial is governed by ethical and regulatory organizations — an institutional review board, the U.S. Food and Drug Administration, and the sponsor of the trial,” says Andrea Tufano-Sugarman, MD, a gynecologic medical oncologist at Memorial Sloan Kettering Cancer Center in Commack, New York. “So using a placebo would not be allowed if it denied patients access to effective therapy.”
Still, there are many misconceptions about placebos and how exactly researchers use them. Here are some common questions and facts about placebos and everything you need to know about them in the context of cancer clinical trials.
Do All Cancer Clinical Trials Involve a Placebo?
No. In fact, most of them don’t. “Oncology patients are almost never given a placebo instead of effective treatment, because it’s just not ethical to withhold an effective treatment from someone,” says Dr. Tufano-Sugarman. The only time people with cancer in a trial might receive a placebo, she says, is in cases when there’s not already a standard of care for the particular type of disease.
“Very rarely — seen more commonly in a phase 1 trial — cancer may not have any treatments that have been proven to be beneficial,” says Shanthi Sivendran, MD, senior vice president for cancer care support at the American Cancer Society. “In those cases, a placebo will be used to show if the new treatment is better than nothing at all.” But it remains extremely rare for placebos to be used as the sole treatment in a trial.
Will I Know If a Trial Involves a Placebo?
In cases where a placebo is used, participants are told about it up front. Information regarding placebo use will be included in the consent form each person reviews and signs before participating in the trial. This is known as the informed consent process.
Consent forms generally outline “the known risks, some unknown risks, and the alternatives to being in this trial,” says Tufano-Sugarman. And, importantly, “It always states that you have the option to withdraw at any time.”
Will I Know If I’m on a Placebo?
It’s possible, but not guaranteed. “In some studies, patients and/or doctors are aware of which treatments are being delivered, and sometimes they do not know,” says Dr. Sivendran. “That’s individual to each study, and it’s important to understand which kind of study you would be part of before participating in the trial.”
A trial in which neither the researcher nor the participant knows their placebo status is called a double-blind trial, which is used to prevent biased study results. In a single-blind trial, the researcher might know which participants are receiving a placebo.
Ask your doctor about this when considering a trial, and look for information confirming it in your informed consent statement, Sivendran advises.
Could a Placebo Make the Cancer Worse?
Because placebos are generally only used in cancer clinical trials when there’s no other standard of care, Sivendran says a placebo will not make the cancer worse than what would be the natural course of the cancer.
And keep in mind, says Tufano-Sugarman, that as a trial participant, you will not be denied effective therapy. “You’re still getting the identical standard-of-care treatments that you would have received if you weren’t in the trial,” she says. In some cases, you may even get access to additional treatments through the trial.
Can I Decline the Placebo and Ask for the Treatment Instead?
In short, no. In a randomized trial, the participants (and doctors) cannot pick which group they are in.
“The goal is that patients are fully informed and truly agreeable to being randomized to either arm of the trial, because there are benefits in being in a clinical trial,” says Tufano-Sugarman, “such as the closer monitoring and the opportunity to perhaps receive a drug they definitely wouldn’t have received otherwise.”
Clinical Trial Participation Can Benefit Your Health and Others’
Placebos are a necessary part of some clinical trials, and as a participant, you’ll still receive the standard of care, even if you are given a placebo. “Participating in a clinical trial can be a really important way to get access to innovative new treatments or combinations of existing treatments,” says Sivendran. Your participation can also help advance cancer care for generations to come. And remember, she adds, “Participation is voluntary and done with your informed consent. You can withdraw from a clinical trial at any point in time.”
The Takeaway
Most cancer clinical trials don’t use a placebo. When a placebo is used, it’s typically only when there’s no existing standard of treatment.
You’ll know if a placebo is being used in a clinical trial before you agree to participate. Details about whether a placebo is involved are explained in advance through the informed consent process.
Your care won’t be compromised in a trial, even if you receive a placebo. Participants continue to receive standard cancer treatment, and you always have the right to leave the study if you’re uncomfortable or your circumstances change.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
ClinicalTrials.gov Glossary Terms: Placebo. ClinicalTrials.gov. May 2025.
Knezevic NN et al. Justice for Placebo: Placebo Effect in Clinical Trials and Everyday Practice. Medicines. February 23, 2025.
Conor E. Steuer, MD, is medical oncologist specializing in the care of aerodigestive cancers, mesothelioma, and thymic malignancies and an assistant professor in the department of hematology and medical oncology at the Emory University School of Medicine in Atlanta. He joined the clinical staff at Emory's Winship Cancer Institute as a practicing physician in July 2015. He currently serves as chair of the Lung and Aerodigestive Malignancies Working Group and is a member of the Discovery and Developmental Therapeutics Research Program at Winship.
Dr. Steuer received his medical degree from the New York University School of Medicine in 2009. He completed his postdoctoral training as a fellow in the department of hematology and medical oncology at the Emory University School of Medicine, where he was chief fellow in his final year.
He has been active in research including in clinical trial development, database analyses, and investigation of molecular biomarkers. He is interested in investigating the molecular biology and genomics of thoracic and head and neck tumors in order to be able to further the care of these patient populations. Additionally, he has taken an interest in utilizing national databases to perform clinical outcomes research, as well as further investigate rare forms of thoracic cancers.
Steuer's work has been published in many leading journals, such as Cancer, the Journal of Thoracic Oncology, and Lung Cancer, and has been presented at multiple international conferences.
Laurel Leicht has been a writer and editor for nearly two decades. A graduate of the College of William and Mary and the master's program at the Missouri School of Journalism, she covers a wide range of health and fitness topics, including breast cancer, various chronic conditions, mental health, and cardiovascular health.
