Abstract
The term nocebo refers to the worse outcomes or side effects experienced by patients as a result of their negative expectations regarding a treatment. It may distort estimates of treatment effectiveness and safety in both clinical trials and clinical practice; moreover, it may cause discontinuation of therapy or drop out from a trial. Nocebo effect is evoked by the information given to patients during a clinical consultation or during enrolment into a study, but information available from the media or the Internet may also play an important role. In research settings, a trial design may introduce bias from the nocebo effect. For example, if the non-treatment group is unblinded and aware that they are not receiving any treatment, their treatment expectations are not met, which results in worse outcomes, and subsequently, the problems that the trial was supposed to investigate may be enhanced in the non-treatment arm. Nocebo effect is common, and its magnitude may be large, but it receives less attention and research focus than the placebo effect. Unlike the placebo effect, which is usually taken into consideration while interpreting treatment results and controlled for in clinical trials, the nocebo effect is under-recognised by clinical researchers as well as clinicians. It is important to recognise and any potential nocebo effect must be considered while assessing the effect of treatment and should be minimised through careful choice and phrasing of treatment-related information given to the patients.
Highlights
Nocebo is often described as placebo’s evil twin, and it rarely gets discussed on its own
There is relatively little research on nocebo and this phenomenon is under-recognised in clinical practice or clinical trials, with many patients and healthcare professionals admitting that they are not aware of its existence (Berthelot et al, 2001)
Nocebo effect is defined as the adverse effect of a placebo intervention, for example placebo hyperalgesia, whereas in clinical or trial settings the term is used to describe the negative outcomes caused by negative expectations, such as lack of efficacy or harm from a drug or other intervention (Benedetti et al, 2007; Hahn, 1997; Häuser et al, 2012)
Summary
Nocebo is often described as placebo’s evil twin, and it rarely gets discussed on its own. These adverse events reported by trial participants but not caused by the pharmacological effects of the tested medication are referred to as the nocebo effect (Barsky et al, 2002) These symptoms are typically generalised and unspecific for example nausea, headaches, fatigue, or irritability. Patients with negative expectations, are more likely to expect adverse events and misattribute them as related to the treatment (Barsky et al, 2002) Some of these symptoms are highly prevalent in populations in which the drug is prescribed, for example, headaches in women taking contraceptive pills (Grimes & Schulz, 2011) or muscle problems in older patients taking statins (Tobert & Newman, 2016). It is important not to leave the patient without treatment, as any type of treatment is better than staying on a waiting list (Khan et al, 2012)
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