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In medicine, a nocebo (Latin for "I shall harm") is an inert substance or form of therapy that creates harmful effects in a patient. The nocebo effect is the adverse reaction experienced by a patient who receives such a therapy. Conversely, a placebo is an inert substance or form of therapy that creates a beneficial response in a patient. The phenomenon by which a placebo creates a beneficial response is called the placebo effect. In contrast to the placebo effect, the nocebo effect is relatively obscure.[1][2]

Both nocebo and placebo effects are presumably psychogenic. Rather than being caused by a biologically active component of the placebo, these reactions might result from a patient's expectations and perceptions of how the substance will affect them. Though they presumably originate from psychological sources, nocebo effects can be either psychological or physiological. Statistical effects like that of the law of large numbers have also been proposed as explanation for both placebo or nocebo.[citation needed]


The term nocebo (Latin nocēbō, "I shall harm", from noceō, "I harm")[3] was coined by Walter Kennedy in 1961 to denote the counterpart of one of the more recent applications of the term placebo (Latin placēbō, "I shall please", from placeō, "I please");[4] a placebo being a substance that produced a beneficial, healthful, pleasant, or desirable effect as a result of the subject's beliefs and expectations, in spite of not containing any active ingredients that could explain these effects.


In the narrowest sense, a nocebo response occurs when a drug-trial subject's symptoms are worsened by the administration of an inert, sham,[5] 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 analgesic effects of anesthetic medications to be abolished.[6]

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."

Although some observers attribute nocebo responses (or placebo responses) to a subject's gullibility, there is no evidence that an individual who manifests a nocebo/placebo response to one treatment will manifest a nocebo/placebo response to any other treatment; i.e., there is no fixed nocebo/placebo-responding trait or propensity.

McGlashan, Evans & Orne (1969, p. 319) found no evidence of what they termed a "placebo personality." Also, in a carefully designed study, Lasagna, Mosteller, von Felsinger and Beecher (1954), found that there was no way that any observer could determine, by testing or by interview, which subject would manifest a placebo reaction and which would not.

Experiments have shown that no relationship exists between an individual's measured hypnotic susceptibility and their manifestation of nocebo or placebo responses.[7]


The term "nocebo response" was coined in 1961 by Walter Kennedy (he actually spoke of a "nocebo reaction").

He had observed that another, entirely different and unrelated, and far more recent meaning of the term "placebo" was emerging into far more common usage in the technical literature (see homonym), namely that a "placebo response" (or "placebo reaction") was a "pleasant" response to a real or sham/dummy treatment (this new and entirely different usage was based on the Latin meaning of the word placebo, "I shall please").

Kennedy chose the Latin word nocebo ("I shall harm") because it was the opposite of the Latin word "placebo", and used it to denote the counterpart of the placebo response: namely, an "unpleasant" response to the application of real or sham treatment.

Kennedy very strongly emphasized that his specific usage of the term "nocebo" did not refer to "the iatrogenic action of drugs":[8] in other words, according to Kennedy, there was no such thing as a "nocebo effect", there was only a "nocebo response".

He insisted that a nocebo reaction was subject-centered, and he was emphatic that the term nocebo reaction specifically referred to "a quality inherent in the patient rather than in the remedy."[8]

Even more significantly, Kennedy also stated that while "nocebo reactions do occur [they should never be confused] with true pharmaceutical effects, such as the ringing in the ears caused by quinine".[8]

This is strong, clear and very persuasive evidence that Kennedy was speaking of an outcome that had been totally generated by a subject's negative expectation of a drug or ritual's administration, which was the exact counterpart of a placebo response that would have been generated by a subject's positive expectation.

Finally, and most definitely, Kennedy was not speaking of an active drug's unwanted but pharmacologically predictable negative side effects (something for which the term nocebo is being increasingly used in current literature).

For example, verbal suggestions of pain induce anxiety, which in turn causes the release of cholecystokinin, which facilitates pain transmission.[9]


Side effects of drugs

It has been shown that, due to the nocebo effect, warning patients about side effects of drugs can contribute to the causation of such effects, whether the drug is real or not.[10][11] This effect has been observed in clinical trials: according to a 2013 review, the dropout rate among placebo-treated patients in a meta-analysis of 41 clinical trials of Parkinson's disease treatments was 8.8%.[12] A 2014 review found that nearly 1 out of 20 patients receiving a placebo in clinical trials for depression dropped out due to adverse events, which were believed to have been caused by the nocebo effect.[13]

Electromagnetic hypersensitivity

Some evidence suggests that the symptoms of electromagnetic hypersensitivity are caused by the nocebo effect.[14][15]


Verbal suggestion can cause hyperalgesia (increased sensitivity to pain) and allodynia (perception of a tactile stimulus as painful) as a result of the nocebo effect.[16] Nocebo hyperalgesia is believed to involve the activation of cholecystokinin receptors.[17]

Ambiguity of medical usage

In a paper,[18] Stewart-Williams and Podd argue that using the contrasting terms "placebo" and "nocebo" to label inert agents that produce pleasant, health-improving, or desirable outcomes versus unpleasant, health-diminishing, or undesirable outcomes (respectively), is extremely counterproductive.

For example, precisely the same inert agents can produce analgesia and hyperalgesia, the first of which, from this definition, would be a placebo, and the second a nocebo.[19]

A second problem is that the same effect, such as immunosuppression, may be desirable for a subject with an autoimmune disorder, but be undesirable for most other subjects. Thus, in the first case, the effect would be a placebo, and in the second, a nocebo.[18]

A third problem is that the prescriber does not know whether the relevant subjects consider the effects that they experience to be desirable or undesirable until some time after the drugs have been administered.[18]

A fourth problem is that the same phenomena are being generated in all the subjects, and these are being generated by the same drug, which is acting in all of the subjects through the same mechanism. Yet because the phenomena in question have been subjectively considered to be desirable to one group but not the other, the phenomena are now being labelled in two mutually exclusive ways (i.e., placebo and nocebo); and this is giving the false impression that the drug in question has produced two different phenomena.[18]

Ambiguity of anthropological usage

Some people maintain that belief kills (e.g., "voodoo death": Cannon (1942) describes a number of "voodoo deaths" from a variety of different cultures) and belief heals (e.g., faith healing).

A "self-willed" death (due to voodoo hex, evil eye, pointing the bone procedure,[20] etc.) is an extreme form of a culture-specific syndrome or mass psychogenic illness that produces a particular form of psychosomatic or psychophysiological disorder which results in a psychogenic death.

Rubel (1964) spoke of "culture bound" syndromes, which were those "from which members of a particular group claim to suffer and for which their culture provides an etiology, diagnosis, preventive measures, and regimens of healing" (p.268).

Certain anthropologists, such as Robert Hahn and Arthur Kleinman, have extended the placebo/nocebo distinction into this realm in order to allow a distinction to be made between rituals, like faith healing, that are performed in order to heal, cure, or bring benefit (placebo rituals) and others, like "pointing the bone", that are performed in order to kill, injure or bring harm (nocebo rituals).

As the meaning of the two inter-related and opposing terms has extended, we now find anthropologists speaking, in various contexts, of nocebo or placebo (harmful or helpful) rituals:

  • that might entail nocebo or placebo (unpleasant or pleasant) procedures;
  • about which subjects might have nocebo or placebo (harmful or beneficial) beliefs;
  • that are delivered by operators that might have nocebo or placebo (pathogenic, disease-generating or salutogenic, health-promoting) expectations;
  • that are delivered to subjects that might have nocebo or placebo (negative, fearful, despairing or positive, hopeful, confident) expectations about the ritual;
  • which are delivered by operators who might have nocebo or placebo (malevolent or benevolent) intentions, in the hope that the rituals will generate nocebo or placebo (lethal, injurious, harmful or restorative, curative, healthy) outcomes;and, that all of this depends upon the operator's overall beliefs in the harmful nature of the nocebo ritual or the beneficial nature of the placebo ritual.

Yet, it may become even more terminologically complex; for, as Hahn and Kleinman indicate, there can also be cases where there are paradoxical nocebo outcomes from placebo rituals (e.g. the TGN1412 drug trial[21][22]), as well as paradoxical placebo outcomes from nocebo rituals (see also unintended consequences).

Writing from his extensive experience of treating cancer (including more than 1,000 melanoma cases) at Sydney Hospital, Milton (1973) warned of the impact of the delivery of a prognosis, and how many of his patients, upon receiving their prognosis, simply turned their face to the wall and died a premature death: "... there is a small group of patients in whom the realization of impending death is a blow so terrible that they are quite unable to adjust to it, and they die rapidly before the malignancy seems to have developed enough to cause death. This problem of self-willed death is in some ways analogous to the death produced in primitive peoples by witchcraft ("Pointing the bone")." (p.1435)

See also


  1. Tavel, Morton E. (February 2014). "The Placebo Effect: The Good, The Bad And The Ugly". The American Journal of Medicine. 127 (6): 484–488. doi:10.1016/j.amjmed.2014.02.002.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  2. Enck, Paul (12 August 2012). "Beware the Nocebo Effect". The New York Times. Retrieved 21 March 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. "Merriam-Webster Online Dictionary". Merriam-Webster. |chapter= ignored (help)<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles> noceo. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  4. Harper, Douglas. "placebo". Online Etymology Dictionary.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles> placeo. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  5. Miller (2003)
  6. Tracey (2011)
  7. McGlashan, Evans & Orne (1969); Stam (1984); Stam & Spanos (1987).
  8. 8.0 8.1 8.2 Kennedy (1961), p.204
  9. Benedetti, F.; Lanotte, M.; Lopiano, L.; Colloca, L. (June 2007). "When words are painful: Unraveling the mechanisms of the nocebo effect". Neuroscience. 147 (2): 260–271. doi:10.1016/j.neuroscience.2007.02.020.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  10. Colloca, Luana; Miller, Franklin G. (September 2011). "The Nocebo Effect and Its Relevance for Clinical Practice". Psychosomatic Medicine. 73 (7): 598–603. doi:10.1097/PSY.0b013e3182294a50.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  11. Barsky, Arthur J. (6 February 2002). "Nonspecific Medication Side Effects and the Nocebo Phenomenon". JAMA. 287 (5): 622. doi:10.1001/jama.287.5.622.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  12. Stathis, P; Smpiliris, M; Konitsiotis, S; Mitsikostas, DD (March 2013). "Nocebo as a potential confounding factor in clinical trials for Parkinson's disease treatment: a meta-analysis". European journal of neurology : the official journal of the European Federation of Neurological Societies. 20 (3): 527–33. doi:10.1111/ene.12014. PMID 23145482.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  13. Mitsikostas, Dimos D.; Mantonakis, Leonidas; Chalarakis, Nikolaos. "Nocebo in clinical trials for depression: A meta-analysis". Psychiatry Research. 215 (1): 82–86. doi:10.1016/j.psychres.2013.10.019.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  14. Rubin, GJ; Nieto-Hernandez, R; Wessely, S (January 2010). "Idiopathic environmental intolerance attributed to electromagnetic fields (formerly 'electromagnetic hypersensitivity'): An updated systematic review of provocation studies". Bioelectromagnetics. 31 (1): 1–11. doi:10.1002/bem.20536. PMID 19681059.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  15. Geary, James (4 March 2010). "The Man Who Was Allergic to Radio Waves". Popular Science. Retrieved 1 December 2014.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  16. Murray, Danielle; Stoessl, A. Jon (December 2013). "Mechanisms and therapeutic implications of the placebo effect in neurological and psychiatric conditions". Pharmacology & Therapeutics. 140 (3): 306–318. doi:10.1016/j.pharmthera.2013.07.009. PMID 23880289.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  17. Enck, Paul; Benedetti, Fabrizio; Schedlowski, Manfred (July 2008). "New Insights into the Placebo and Nocebo Responses". Neuron. 59 (2): 195–206. doi:10.1016/j.neuron.2008.06.030.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  18. 18.0 18.1 18.2 18.3 Stewart-Williams & Podd (2004), p.326
  19. Colloca, L; Benedetti, F (October 2007). "Nocebo hyperalgesia: how anxiety is turned into pain". Current opinion in anaesthesiology. 20 (5): 435–9. doi:10.1097/aco.0b013e3282b972fb. PMID 17873596.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  20. Zusne & Jones (1989), p.57; Róheim (1925).
  21. "New drug trial puts six men in intensive care". New Scientist. 15 March 2006. Retrieved 11 February 2012.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  22. "Catastrophic immune response may have caused drug trial horror". New Scientist. 17 March 2006. Retrieved 11 February 2012.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>


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