Placebo Effect

The placebo effect is an improvement in an individual's medical condition or an alleviation of adverse symptoms that occurs when the person receives an inert treatment. It may result from the person's expectation of improvement or from the increased motivation to make improvements in general health that may result. The placebo effect was first described in 1955 by Henry K. Beecher, an American physician, who described it in his frequently cited article, ‘The Powerful Placebo.’ The placebo effect has been explained as a result of the Pavlovian conditioning theory, the expectancy-value theory, and increased motivation on the part of the participant.

A placebo may be contact with a physician, cognitive or behavioral intervention, lifestyle changes in diet or level of physical activity, or a sugar pill. Regardless of the form, the aim of a placebo is to have no biologic effect at all. Placebos are typically used in placebocontrolled clinical trials where a treatment group receives the medical intervention being tested and the control group receives a placebo. The aim of this experimental design is to ensure that the study participants do not know whether they are receiving the treatment or the placebo. When the experimenter knows who is receiving the treatment and who is receiving the placebo, the study is single blind; if neither the participants nor the researcher knows, the study is double blind. Such studies minimize potential bias that may distort the true relationship between the exposure to the treatment and the outcome.

Although the aim of a placebo is primarily related to improving the methodology of a trial by blinding the participants to the status of the received treatments, one of the results of offering a placebo is that some individuals actually feel better and experience a beneficial effect despite the fact that the placebo has no known mechanism of action that may induce this effect. It seems that for illnesses such as depression, headache, stomach ailments, and pain, about a third of patients taking a placebo actually start to feel better because they believe they are receiving medical treatment, when in fact they are receiving an inert treatment.

The biologic mechanism by which a placebo can create this effect is unclear. However, it has been suggested that it is primarily a psychological effect that results from the individual's expectation that the treatment will work. Another theory of the mechanism of the placebo effect is that it is a conditioned response reflecting people's experience of treatment followed by symptom relief.

There are several ethical issues in the use of a placebo. Some bioethicists suggest that patients participating in trials cannot truly give informed consent if they do not know which treatment they will be receiving. Another criticism is that single-blind studies introduce an element of deception into health care and practice, because patients are told or allowed to believe that they are receiving a drug when the researchers know otherwise. Furthermore, in some cases, the placebo effect may actually result in adverse side effects, rather than only beneficial ones; this phenomenon is often called the nocebo effect. This may occur when individuals expect to experience negative side effects from the treatment.

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