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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Nocebo | 1/2 | https://en.wikipedia.org/wiki/Nocebo | reference | science, encyclopedia | 2026-05-05T07:31:12.972595+00:00 | kb-cron |
A nocebo effect is said to occur when a patient's expectations for a treatment cause the treatment to have a worse effect than it otherwise would have. For example, when a patient anticipates a side effect of a medication, they can experience that effect even if the "medication" is actually an inert substance. The complementary concept, the placebo effect, is said to occur when expectations improve an outcome.
More generally, the nocebo effect is falling ill simply by consciously or subconsciously anticipating a harmful event. This definition includes anticipated events other than medical treatment. It has been applied to Havana syndrome, where purported victims were anticipating attacks by foreign adversaries. This definition also applies to cases of electromagnetic hypersensitivity.
Both placebo and nocebo effects are presumably psychogenic but can induce measurable changes in the body. 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.
== Etymology and usage == Walter Kennedy coined the term nocebo (Latin nocēbō, "I shall harm", from noceō, "I harm") in 1961 to denote the counterpart of placebo (Latin placēbō, "I shall please", from placeō, "I please"), a substance that may produce a beneficial, healthful, pleasant, or desirable effect. Kennedy emphasized that his use of the term nocebo refers strictly to a subject-centered response, a quality "inherent in the patient rather than in the remedy". That is, he rejected the use of the term for pharmacologically induced negative side effects such as the ringing in the ears caused by quinine. That is not to say that the patient's psychologically induced response may not include physiological effects. For example, an expectation of pain may induce anxiety, which in turn causes the release of cholecystokinin, which facilitates pain transmission.
== Response == 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. Placebos contain no chemicals (or any other agents) that could cause any of the observed worsening in the subject's symptoms, so any change for the worse must be due to some subjective factor. Adverse expectations can also cause anesthetic medications' analgesic effects 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 the placebo has not chemically generated those symptoms. Because this generation of symptoms entails a complex of "subject-internal" activities, we can never speak in the strictest sense in terms of simulator-centered "nocebo effects", but only in terms of subject-centered "nocebo responses". Some observers attribute nocebo responses (or placebo responses) to a subject's gullibility, but there is no evidence that someone 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. Based on a biosemiotic model (2022), Goli explains how harm and/or healing expectations lead to a multimodal image and form transient allostatic or homeostatic interoceptive feelings, demonstrating how repetitive experiences of a potential body induce epigenetic changes and form new attractors, such as nocebos and placeboes, in the actual body.
== Effects ==
=== Side effects of drugs === It has been shown that, due to the nocebo effect, warning patients about drugs' side effects can contribute to the causation of such effects, whether the drug is real or not. 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%. A 2013 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. In January 2022, a systematic review and meta-analysis concluded that nocebo responses accounted for 72% of adverse effects after the first COVID-19 vaccine dose and 52% after the second dose. Many studies show that the formation of nocebo responses are influenced by inappropriate health education, media work, and other discourse makers who induce health anxiety and negative expectations. Researchers studying the side effects of statins in UK determined that a large proportion of reported side effects were related not to any pharmacological cause but to the nocebo effect. In the UK, publicity in 2013 about the apparent side effects caused hundreds of thousands of patients to stop taking statins, leading to an estimated 2,000 additional cardiovascular events in the subsequent years.
=== Electromagnetic hypersensitivity === Evidence suggests that the symptoms of electromagnetic hypersensitivity are caused by the nocebo effect.
=== Pain === 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. Nocebo hyperalgesia is believed to involve the activation of cholecystokinin receptors.