The Placebo Effect: Mind over Matter

An individual receives an injection from his or her doctor to reduce the discomfort caused by a recurrence of rheumatoid arthritis. The physician, in line with an ethical obligation, has already explained to the patient that he or she will be the beneficiary of either an effective new drug that is in the final stages of research or a placebo. After taking the medicine, the individual reports that the pain and stiffness have eased and that the swelling and inflammation have objectively improved. What the patient does not know is that the only ingredient in the shot was an inactive saline solution. The individual was given a placebo, and what he or she experienced was the placebo effect.

A placebo is an intervention (pill, injection, or treatment) that has no inherent healing or transforming properties. The placebo effect, the body's biochemical response to this inert intervention, is initiated by a suggestion made to the mind. In other words, the imagination has curative powers.

Although placebos have always had a place in medicine, ethical controversy has long surrounded their use. References to the healing power of symbols and belief systems predate Hippocrates, but it was not until 1811 that a definition of the word placebo appeared in medical literature. In 1834 placebos were first used as a control in a scientific study; this has since become their predominant role in medicine.

In research it is essential to separate any contaminating effects of the procedure from those of the active experimental (treatment) agent. In one commonly used method for controlling contaminants, the double-blind approach, suitable volunteers are assigned to either an experimental group or a placebo group. Neither the investigators nor the subjects are aware of individual group affiliations. The placebo subjects are exposed to the exact same protocol, receive the same attention, and have the same expectations as the experimental subjects. Any differences in outcome between the two groups can therefore be directly attributed to the treatment agent, since all other aspects of the experiment are identical.

Although it has been established that placebos have been effective in reducing pain, lowering cholesterol and blood pressure, relieving insomnia and depression, and even shrinking tumors, the phenomenon can work in an undesirable manner as well (sometimes called the "nocebo" effect). Take, for example, the individual who develops symptoms of the rumored negative side effects of a drug that he or she has not actually received or the person who starts to hallucinate after falsely believing that a mind-altering substance has been ingested.

Clearly, expectations, setting, and past experiences are essential components in determining the strength and direction of the placebo effect.

What about individual differences? Are some people more susceptible to placebos than others? Is there a placebo-responder personality? Are there situations or states of mind that make people more vulnerable to the power of the placebo? The answer to all of these questions is yes. Studies indicate that the person who exhibits a profile that reflects the qualities of open-mindedness, trust, extroversion, compliance, and suggestibility will be more responsive. Moreover, individuals in an anxious or uninhibited state also are more sensitive to a placebo's effects.

In order to explain how placebos work on a cellular level, scientists turn to the branch of medicine known as psychoneuroimmunology, which, as its name implies, combines the disciplines of psychology, neurology, and immunology. The two basic axioms of this field are that every change in thought almost simultaneously creates variations in physiology, and that the body has an innate ability to spontaneously heal itself. An individual's expectations, social context, and past learning experiences induce a pattern of involuntary bodily responses based on classical conditioning that influence the autonomic, central nervous, and endocrine systems. If the mind believes that an intervention will produce a certain effect, the internal organs, including the immune system, or "internal pharmacy," will act in concert, in much the same way that Pavlov's dog salivated at the sound of a bell.