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Placebo, nocebo, and contextual effects 

Placebo, nocebo, and contextual effects
Chapter:
Placebo, nocebo, and contextual effects
Author(s):

Abhishek Abhishek

and Michael Doherty

DOI:
10.1093/med/9780199668847.003.0027
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date: 30 October 2020

Placebo effect is an example of ‘contextual’ effect and is the symptomatic improvement experienced by patients who have unknowingly received a placebo (inactive treatment) instead of an active drug. It occurs due to patient-specific factors such as expectation of improvement and is influenced by the context in which the treatment is delivered. Nocebo effect is the opposite of placebo effect and includes worsening of symptoms or incident adverse effects due to expectancy or negative contextual or practitioner influence. Placebo effect has been demonstrated in a range of musculoskeletal conditions, including osteoarthritis (OA), as well as other conditions such as Parkinson’s disease, irritable bowel syndrome, and asthma. In OA, the placebo effect is strongest for subjective outcomes like pain. In fact, the effect size (ES) of placebo analgesia in OA clinical trials (0.51) is clinically significant and higher than the ES (defined by the additional improvement above placebo) obtained from non-pharmacological (0.25) and pharmacological (0.39) treatments. A number of patient- and intervention-specific and contextual factors influence the magnitude of placebo-induced improvements. Placebo analgesia is real, not a ‘trick of the mind’, and results from central mechanisms that increase descending inhibition of pain. Contextual effects are an integral part of everyday clinical practice. While patient- and intervention-specific determinants cannot be changed easily, healthcare practitioners should optimize the physician-specific factors that enhance positive contextual response and minimize nocebo response. Such a strategy that will increase the overall improvement is particularly relevant for OA where there is no ‘cure’ and a predominance of negative beliefs.

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