Placebo Effect

Placebo Effect Definition

Placebo EffectA placebo is a medical term for a drug that has no active ingredient. Biologically, it doesn’t do anything, but the patient might mistakenly believe it is a powerful medicine. In fact, in bygone eras, some people who took snake oil and other medically useless substances did get better, partly because they believed that these substances would cure them. The phrase placebo effect refers to a person’s response to a substance only as the result of the expectation of such a response.

The response is called a placebo effect when the substance is known not to induce any response, but a consistent response is found. Because of the placebo effect, people may experience or perceive the effects of medication, such as pain relief or psychotropic effects, even when the “medication” given to them is merely an inert dose that the patient believes to be medicinal (i.e., a pill or serum with no reagent). Placebo effects are one category of expectation effects, though not all expectancy effects are placebo effects because people may expect any outcome for any reason, whether or not they have been given a placebo.

Placebo Effect History and Modern Usage

The word placebo, in Vulgate Latin, referred to pleasing or satisfying some need or desire. Adopted by the medical community, the term referred to a “drug” given to satisfy a patient’s desire for a drug, without giving the patient the actual drug. Because many medications may have negative side effects, doctors began prescribing pills with no medicinal content, informing patients that the pills were indeed the drug they sought. In this manner, patients were satisfied without being exposed to unnecessary, potentially dangerous drugs. These pills were often made out of sugar, and for this reason placebos are often referred to as sugar pills.

Doctors found, however, that some patients who were given these inert pills responded to the treatments, reporting that their symptoms had improved or ceased! Because the “medications” prescribed could not be lauded for the improvements, psychological expectations were used to explain the patients’ responses, and still are. People have shown placebo effects for medications expected to relieve pain, prevent heart attacks, heal injuries, and reduce symptoms for depression. Though placebo effects are rarely as effective as actual medication, it is nonetheless impressive that people feel and exhibit responses to nothing more than their expectations.

Today, medical researchers take special care to test for placebo effects by using “double blind” experiments: giving all subjects pills that appear identical, but ensuring that some subjects receive the real drug while others receive a placebo. When neither the subject nor the provider knows whether the subject is getting a real pill or a placebo, all subjects have the same expectations. As such, differences in outcome between subjects who receive real medication and subjects who do not cannot be caused by differences in expectation. Comparing these two groups to subjects in a third “control” condition, in which subjects have been given no treatment (not even a sugar pill) nor told to expect any results, allows researchers to test whether there is a placebo effect present.

Some theorists suggest that placebo effects are physiological responses induced by the placebo. Others hypothesize that motivations (e.g., to please a doctor), or simply expectations alone may cause placebo effects.


  • White, L., Tursky, B., & Schwartz, G. (1985). Placebo: Theory, research, and mechanisms. New York: Guilford Press.

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