A placebo (pluh-see-bow) is a substance or other kind of treatment that looks just like a regular treatment or medicine, but is not. It is actually an inactive "look-alike" treatment or substance. This means that it is not a medicine. The person who is getting a placebo does not know he or she is getting one. Sometimes the placebo is in the form of a "sugar pill," but a placebo can also be an injection, a liquid, a procedure, or any other type of therapy that doesn't directly affect the illness being treated.

Even though placebos do not act on the disease, they seem to have an effect in about 1 out of 3 patients. A change in a person's symptoms as a result of getting a placebo is called a placebo effect. This effect usually lasts only a short time, and is thought have something to do with the body's own chemical ability to temporarily relieve pain or certain other symptoms.

Usually the term placebo effect refers to the helpful effects of a placebo in relieving symptoms. Sometimes, however, the effect goes in the opposite direction and causes unpleasant or worse symptoms. These may include symptoms like headaches, nervousness, nausea, and constipation, to name a few. The unpleasant effects that happen after getting a placebo or an inactive treatment are sometimes called the nocebo effect.

Together, these 2 types of outcomes are known as expectation effects. This means that the person taking the placebo may experience something along the lines of what he or she expects to happen. If a person expects to feel better, that may happen. If the person thinks that he or she is getting a strong medicine, the placebo may be thought to cause the side effects. The placebo does not cause any of these effects directly. Instead, the person's belief in or experience of the placebo is responsible for the change in symptoms.

Along with the placebo or nocebo effect, incidental events (unrelated effects that may have happened without the placebo) may also be linked to the placebo because of a person's expectation. For example, a headache or rash that happens soon after taking a placebo may be caused by something else entirely, but the person may think the placebo caused it. The same can be said for good outcomes: if a person happened to start feeling better after taking a placebo, that improvement may be thought to be due to the placebo.

Some patients can have a placebo effect without getting an actual placebo. Some may just feel better from visiting the doctor or doing something else they believe in. That type of placebo effect seems most related to the degree of confidence and faith the patient has in the doctor or activity.

How are placebos used?

Placebos are often used in clinical trials to test new medicines or treatments. Clinical trials are research studies testing new drugs or other treatments in people. Before a new treatment is used on people, it is studied in the lab. If lab studies suggest the treatment will work, the next step is to test it on animals. If that also gives promising results, it may then be tested in clinical trials to see if it has value for patients. The main questions the researchers want to answer are:

• Does this treatment work? 
• Does it work better than what we're now using? 
• What side effects does it cause? 
• Do the benefits outweigh the risks? 
• Which patients are most likely to find this treatment helpful?

If standard treatments for the disease are already available, the new treatment is usually compared to one of these treatments. This tells researchers if the new treatment is as good as or better than the one that is currently available. If you would like to know more about this type of study, see the Additional resources section to find out how to get the American Cancer Society document Clinical Trials: What You Need to Know.

If there is no approved treatment for an illness or condition, some people in the study may be given a placebo, while others get the new treatment being tested. The main reason to have a placebo group is to be sure that any effects that happen are actually caused by the treatment and not some other factor. The placebo looks, tastes, or feels just like the actual treatment. In a "double-blind controlled study," neither the people taking part in the study nor their doctors know who is getting which treatment.

People in a study that involves a placebo should always know that there is a chance they could be getting a placebo. It is not OK to give someone a treatment in a clinical trial and not mention that it could be a placebo. The American Cancer Society document Informed Consent gives you more information on this topic. Go to the Additional resources section to find out how to get a copy.

Those who get placebos in medical studies serve an important role. Their responses help provide an accurate way to determine the effect of the treatment being tested. The placebo group provides an important baseline to compare the treatment group against. It helps researchers see what would have happened without the treatment. For instance, illnesses that sometimes go away on their own might be thought to get better because of the medicine, unless there is a placebo group and those people also get better. On the other side, bad effects that were going to happen anyway, or that occur from some unrelated cause, may be blamed on the treatment unless they also happen to people in the placebo group.

How does the placebo effect work?

In the past, some researchers have questioned whether there is convincing proof that the placebo effect is a real effect. But there are studies indicating that the placebo effect is real. For example, scientists have recorded brain activity responding to placebo.

Many think the placebo effect occurs because the patient believes in the substance, the treatment, or the doctor. The patient's mind somehow causes other physical changes in the body. The patient expects to feel better, and therefore he or she does feel better. If a person feels better after taking a placebo, however, it doesn't necessarily mean the person's illness or symptoms were not real.

Since many scientific tests have shown the placebo effect, it is one way we know for sure that the mind and body are connected. Some scientific evidence suggests that the placebo effect may be partly due to the release of endorphins in the brain. Endorphins are the body's natural pain killers. There is probably more to it than this, however.

What is commonly called the placebo effect even plays a role in mainstream medicine. Many people feel better after they get medical treatments when they expect them to work. But the opposite can also happen and this seems to support the idea of the expectation effect even more. For example, in one study, people with Alzheimer's disease were less affected by pain medicines, and required higher doses--possibly because they had forgotten they were getting the drugs, or that the pain medicines had worked for them before.

Although we may not know exactly how it works, the idea that the mind can affect the body has been around for years and is well-proven in certain situations. Many ancient cultures depended on mind-body connections to treat illness. Shamans or medicine men would not have viewed their efforts as placebos. However, their healing powers may have worked in the same way, partly through the patient's strong belief that the shaman's treatments would restore health. Or it could be that the sick person was going to get better anyway, but the recovery was thought to be because of the treatment--which may have done nothing for the illness.

Because placebos often have an effect, even if it does not last long, some people think that the placebo produced a "cure." But placebos do not cure. They clearly can help relieve certain symptoms such as pain, depression, and insomnia in some people. In earlier times, placebos were sometimes given by doctors out of frustration or desperation in trying to treat a patient's symptoms when nothing else was available or seemed to work.

Sometimes if the placebo looks more "real", the person may think it is an active medicine or treatment and believe in its power even more. For example, a larger pill may look more powerful than a small pill. In some people, an injection may have a stronger placebo effect than a pill.

Some believe that placebos seem to work because many illnesses improve over time even without treatment. People may also take better care of themselves by exercising, eating healthier, or resting if they are taking a placebo. Just as natural endorphins may relieve pain once they are released, some research shows the brain may respond to an imagined scene much as it would to something it actually sees. A placebo may help the brain remember a time before the symptoms and bring about a chemical change. This is a theory called remembered wellness.

Some scientists believe that the effects of many alternative therapies may simply be a placebo effect. If the patient believes in the treatment and wants it to work, it can seem to do so, at least for a while. If this effect worked on an illness that usually would not get better on its own, and it lasted, it would be considered a real cure, not a placebo.

There is still much to learn about the placebo effect and how it may work. Scientists will continue to study this interesting mystery in hopes of unveiling more about it.

Additional resources

More information from your American Cancer Society

The following related information may also be helpful to you. These materials may be viewed on our Web site or ordered from our toll-free number, 1-800-ACS-2345.

Clinical Trials: What You Need to Know

Complementary and Alternative Methods for Cancer Management

Dietary Supplements: How to Know What Is Safe

Guidelines for Using Complementary and Alternative Methods

Informed Consent

American Cancer Society Operational Statement on Complementary and Alternative Methods of Cancer Management

In addition to the above, information on many different types of complementary and alternative treatments are available at no cost to you from the American Cancer Society. You can find them on our Web site or order from our toll-free number as noted above.

National organizations and Web sites*

There is a great deal of interest today in complementary and alternative therapies. Mass communication, especially the Internet, makes it possible for people to share ideas and information very quickly. But too often information on the Internet is written by promoters of useless treatments. In addition to the American Cancer Society, the following is a partial list of Web sites and phone numbers of reputable groups that provide information on complementary and alternative therapies:

National Cancer Institute (NCI)
Web site: http://www.cancer.gov
Toll-free number: 1-800-422-6237 (1-800-4-CANCER)
TTY: 1-800-332-8615

National Center for Complementary and Alternative Medicine (NCCAM)
Web site: http://nccam.nih.gov
Toll-free number: 1-888-644-6226
TTY: 1-866-464-3615

Memorial Sloan Kettering Cancer Center
About Herbs and Botanicals
Web site: http://www.mskcc.org/mskcc/html/11570.cfm

The University of Texas MD Anderson Center
Complementary/Integrative Medicine Therapies
Web site: http://www.mdanderson.org/cimer

United States Department of Agriculture, Food and Nutrition Information Center
Web site: http://fnic.nal.usda.gov
Choose "Dietary Supplements" from the left menu bar

United States Food and Drug Administration
Web site: http://vm.cfsan.fda.gov/%7Edms/supplmnt.html
Toll-free number: 1-888-INFO-FDA (1-888-463-6332)
To report side effects or other adverse events from a dietary supplement, call Medwatch at 1-800-FDA-1088

National Council Against Health Fraud
Web site: http://www.ncahf.org

Quackwatch
Web site: http://www.quackwatch.org

*Inclusion on this list does not imply endorsement by the American Cancer Society

No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-ACS-2345 or visit www.cancer.org.

References

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Beyerstein BL. Distinguishing science from pseudoscience. 1995. Victoria, B.C.: The Centre for Curriculum and Professional Development. Available at: http://www.sfu.ca/~beyerste/research/articles/02SciencevsPseudoscience.pdf. Accessed November 8, 2007.

Haour, F. Mechanisms of the placebo effect and of conditioning. Neuroimmunomodulation. 2005;12:195-200.

Hrobjartsson A, Gotzsche PC. Is the placebo powerless? Systematic review with 52 new randomized trials comparing placebo with no treatment. Journal of Internal Medicine. 2005;257:394-396.

Kaptchuk TJ. The placebo effect in alternative medicine: Can the performance of a healing ritual have clinical significance? Ann Intern Med. 2002;136:817-825.

Link J, Haggard R, Kelly K, Forrer D. Placebo/nocebo symptom reporting in a sham herbal supplement trial. Eval Health Prof. 2006;29:394-406.

Wampold, BE, Minami T, Tierney SC , Baskin TW, Bhati, KS. The placebo is powerful: Estimating placebo effects in medicine and psychotherapy from randomized clinical trials. Journal of Clinical Psychology. 2005;61:835-854.

The Australian Psychological Society. Placebo effect. Last updated March 2006. Available at: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Placebo_effect?OpenDocument. Accessed December 13, 2007.

Scott DJ, Stohler CS, Egnatuk CM, et al. Individual differences in reward responding explain placebo-induced expectations and effects. Neuron. 2007;55:325-336.

Wager TD, Rilling JK, Smith EE, et al. Placebo-induced changes in fMRI in the anticipation and experience of pain. Science. 2004;303:1162-1167.

Revised: 01/18/2008