Placebo effect


A placebo effect occurs when a treatment or medication with no therapeutic value (a placebo) is administered to a patient and the patient's symptoms improve. The patient believes and expects that the treatment is going to work, therefore it does. The placebo effect is also a factor to some degree in clinically effective therapies, and explains why patients respond better than others to treatment despite similar symptoms and illnesses.


The word placebo is from the Latin "I shall please." Throughout most of medical history, the placebo effect was the principal treatment physicians offered their patients—e.g. reassurance, attention, and belief in treatment would mobilize patients' internal powers to fight their illnesses. This is still true in indigenous cultures using shamanistic healing which places healing power in objects and rituals. In fact placebos are sometimes called sham treatments.

Placebos were used throughout the nineteenth century in blind assessments of medical treatments. These blind assessments were created to test controversial medical treatments of the time (e.g. mesmerism and homeopathy), and involved using a blindfold on or withholding information from patients so they were unaware of the exact nature of the treatment being studied. For example, in blind assessments of homeopathy conducted in 1834 in France, homeopathic remedies were replaced with an inert placebo substance without the patient's knowledge. These blind assessments were the forerunners to today's double-blind randomized controlled trials used in drug development and in the study of other therapeutic techniques.

According to some medical historians, from the early 1800s through as late as World War II, placebos (usually in the form of sugar pills or saline injections) were regularly prescribed to up to 80% of patients. Doctors used placebos to appease patients when no effective treatment for their symptoms was available, or prescribed placebos to patients they perceived as difficult.

The first documented American clinical study using placebos was conducted in the late 1920s. In 1937 scientists at Cornell University Medical School published a study on an angina drug that used a placebo and blind assessment techniques. They found that the patients who were given a placebo instead of the angina drug experienced an improvement of symptoms. This was the first published account in the United States that discussed the possible therapeutic value of the placebo effect.


The placebo effect is usually positive by its nature, because it indicates that a patient believes in the therapy, and the therapy is having some sort of a beneficial effect. The placebo effect has been documented in a wide variety of diseases and disorders. Certain conditions such as headaches, arthritis, and hot flashes are especially responsive to placebos, as are some individuals.


Every available medical treatment is subject to the placebo effect. If a patient believes the therapy will benefit them, it usually will to some degree. Even if the placebo does not improve the symptoms directly, the peace of mind a patient may feel after taking a treatment they believe will help them is often enough to encourage a sense of improved well-being. This is why controlled, scientific studies are so crucial to determining the actual clinical efficacy of medications and therapies.

The person prescribing the placebo treatment may also have an impact on the effect it has on the patient. For example, a doctor's enthusiasm about a new treatment may heighten its placebo effect for his patient. In addition, if a healthcare provider is perceived as a trusted, well-respected figure by the patient, the patient may experience benefits from any treatments the provider prescribes.

Placebos are often used in scientific trials of new medications and treatments to determine their efficacy. A randomly selected group of study subjects known as the control group are given placebo medication (usually a sugar or water-based substance) or treatment while the rest of the subjects are administered the actual therapy. The patients do not know which group they are in during the study, and the researchers and study authors do not know which subjects are in which group (hence the term double-blind). This helps researchers to determine if new treatments work because they are clinically effective, or because the subjects believe they will work.

Overall, the average placebo effect is 33%, though it can range lower and higher. Therefore, to demonstrate that a treatment, procedure, or medication is effective, a trial has to show that it does significantly better than the placebo given to a control group. For example, a study of single-remedy homeopathy was conducted with a group of 487 patients with an influenza-like syndrome. Patients treated with a single, non-individualized remedy were 70% more likely to have recovered within 48 hours than those receiving the placebo.


Placebos only have therapeutic value if the patient believes they will work. If an individual chooses a healthcare provider that they trust, respect, and feel comfortable with, there may be a more likely chance that treatments the provider recommends (whether clinically effective or unproven) will be perceived as having a more beneficial effect.

The use of a placebo in scientific studies requires informed consent of the entire population of subjects. The study subjects must know that they have a 50/50 chance of receiving a placebo treatment instead of the treatment under investigation.


There are ethical issues involved with administering placebos to patients if the healthcare provider knows there is no therapeutic value to the treatment and other available treatments could possibly benefit the patient. For patients with progressive or life-threatening illnesses, taking a medication or therapy with no clinical value other than its placebo effect can be harmful if it causes them to neglect other proven treatments that could improve their condition.

Some clinical trials of surgical procedures require the placebo, or control subjects to undergo what is essentially unnecessary surgery, involving incisions and other invasive procedures while the final therapeutic portion of the procedure is withheld (the placebo). Although this is standard scientific procedure currently recommended by the U.S. Food and Drug Administration (FDA) for the approval of new medical procedures and devices, it is also commonly accepted knowledge that unnecessary surgery is never beneficial to a patient and can result in serious complications such as infection, hemorrhaging, and conceivably even death.

Side effects

The placebo effect can have a negative influence also, a nocebo. If a placebo is given that the patient believes to be harmful to their health in some way, he or she may develop symptoms appropriate to this belief. A toxic or negative placebo suggests the great degree to which attitudes and expectations can affect one's state of health or course of an illness. People who think they have been cursed or a victim of voodoo have been known to die.

Research & general acceptance

The placebo effect is a well-known phenomena in the scientific community, and clinical trials and other scientific studies are built around the theory. Ethical concerns can arise when there is a risk that patients are not getting the potentially life-saving treatments they need. In some cases, the placebo effect is enough to compensate for this. For example, a study published in the Archives of General Psychiatry found that in 45 controlled trials of antidepressants, subjects in the control group experienced a significant positive therapeutic effect with the placebo only. In cases of treatments involving potentially fatal diseases such as cancer and AIDS, the ethical implications of placebo use may not be as clear-cut.

Surgical placebo procedures, which are a relatively new type of clinical study, are not as universally accepted as placebo drug trials. There is a heated debate in the medical community over the value of such studies. However, the use of placebo surgery for controlled clinical trials is endorsed by the National Institutes of Health, the medical research arm of the U.S. Department of Health and Human Services.



Harrington, Anne. The Placebo Effect: An Interdisciplinary Exploration. Cambridge, MA: Harvard University Press, 1999.

Shapiro, Arthur K., and Elaine Shapiro. The Powerful Placebo: From Ancient Priest to Modern Physician. Baltimore, MD: John Hopkins University Press, 1997.


Kaptchuk, Ted J. "Intentional Ignorance: A History of Blind Assessment and Placebo Controls in Medicine." Bulletin of the History of Medicine 72, no. 3 (1998):389-433.

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