Abstract
The term nocebo effect refers to the harmful outcomes that result from people's negative beliefs, anticipations, or experiences related to the treatment rather than the pharmacological properties of the treatment. These outcomes may include a worsening of symptoms, a lack of expected improvement, or adverse events, and they may occur after the active treatment and the placebo that is supposed to imitate it. The nocebo effect is always unwanted and may distort estimates of treatment effectiveness and safety; moreover, it may causediscontinuation of therapy or withdrawal from a trial. The nocebo effect may be unintentionally evoked by the explanations given by healthcare professionals during a clinical consultation or consent procedures, or by information from other patients, the media, or the Internet. Moreover, it may be a consequence of previous bad experiences with the treatment, through learning and conditioning, and the conditioning may happen without patients' conscious awareness. In trial settings, a study design, for example lack of blinding, may introduce bias from the nocebo effect. Unlike the placebo effect, which is usually taken into consideration while interpreting treatment outcomes and controlled for in clinical trials, the nocebo effect is under-recognised by clinical researchers and clinicians. This is worrying, because the nocebo phenomenon is common and may have potentially negative consequences for the results of clinical treatment and trials. It is therefore important that doctors and medical researchers consider any potential nocebo effect while assessing the treatment effect and try to minimise it through careful choice and phrasing of treatment-related information given to patients.
Highlights
Nocebo is often described as placebo’s evil twin, and is rarely discussed on its own
The nocebo effect is defined as the adverse effects of an intervention that are not related to its pharmacological or physiological effects
In clinical or trial settings, the term is used to describe the negative effects produced by placebos or either harm or lack of efficacy of the active intervention (Benedetti et al, 2007; Hahn, 1997; Häuser et al, 2012)
Summary
Nocebo is often described as placebo’s evil twin, and is rarely discussed on its own. Nebulised saline evoked asthma attacks in patients with asthma if it was given with information that contained an irritant, while the same saline relieved the symptoms if it was presented as an active treatment (Luparello et al, 1968) This is important in the context of clinical trials, as a patient may be asked to record any unusual symptoms and the doctor, who may not know the patient’s long-term clinical history, may be more likely to interpret any new symptom as an adverse effect of the medication. The nocebo effect can be prevented by careful phrasing and positive framing of the information given to patients, for example by focusing on chances of improvement, survival, being symptom-free, and of not developing adverse effects (Crichton & Petrie, 2015) Another way to reduce the nocebo effect is to ask patients about their preconceptions and beliefs regarding a treatment or about previous experiences as they may negatively affect treatment outcomes. When patients expect to feel worse or not to improve, they treat every negative sensation as being caused by the treatment, and so they do not take the treatment regularly or stop it altogether, which in turn results in a subtherapeutic dose of medication
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