Nocebo

The nocebo effect is when a negative expectation of a phenomenon causes it to have a more negative effect than it otherwise would. A nocebo effect causes the perception that the phenomenon will have a negative outcome to actively influence the result. Mental states such as beliefs, expectations and anticipation can strongly influence the outcome of: disease; experience of pain; and even success of surgery. Positive expectations regarding a treatment can result in more positive outcomes and this effect is known as the placebo effect. Both placebo and nocebo effects are presumably but also produce measurable physiological changes as well as changes in the brain, the body and behavior. For example, when a patient anticipates a side effect of a treatment, he/she can suffer them even if the medication provided is an inert substance. One article that reviewed 31 studies on nocebo effects reported a wide range of symptoms that could manifest as nocebo effects including nausea, stomach pains, itching, bloating, depression, sleep problems, loss of appetite, sexual dysfunction and severe hypotension.

The term nocebo (Latin , "I shall harm", from , "I harm") was coined by Walter Kennedy in 1961 to denote the counterpart to the use of placebo (Latin , "I shall please", from , "I please"); as a substance that may produce a beneficial, healthful, pleasant, or desirable effect.

In the narrowest sense, a nocebo response occurs when a drug-trial subject's symptoms are worsened by the administration of an inert, sham, or dummy (simulator) treatment, called a placebo.

According to current pharmacological knowledge and the current understanding of cause and effect, a placebo contains no chemical (or any other agent) that could possibly cause any of the observed worsening in the subject's symptoms. Thus, any change for the worse must be due to some subjective factor.

Adverse expectations can also cause the analgesic effects of anesthetic medications to disappear.

The worsening of the subject's symptoms or reduction of beneficial effects is a direct consequence of their exposure to the placebo, but those symptoms have not been chemically generated by the placebo. Because this generation of symptoms entails a complex of "subject-internal" activities, in the strictest sense, we can never speak in terms of simulator-centered "nocebo effects," but only in terms of subject-centered "nocebo responses."

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