(HealthDay News) – The nocebo effect, or induction of a symptom perceived as negative by sham treatment and/or the suggestion of negative expectation, may arise from suggestions by doctors and nurses, according to a study published in Deutsches Ärzteblatt International.

Winfried Häuser, MD, from Technische Universität München, and colleagues conducted a literature review to investigate nocebo phenomena in clinical practice.

The researchers found that the underlying mechanisms behind nocebo responses included learning by Pavlovian conditioning and reaction to expectations induced by verbal information or suggestion. Unintentional negative suggestion on the part of physicians and nurses was found to trigger nocebo responses. The patients’ negative expectations, along with being given information about possible complications, increased the likelihood of adverse effects. A nocebo effect was found to cause adverse events under treatment with medications.

“Physicians face an ethical dilemma, as they are required not just to inform patients of the potential complications of treatment, but also to minimize the likelihood of these complications, ie, to avoid inducing them through the potential nocebo effect of thorough patient information,” the authors write. “Possible ways out of the dilemma include emphasizing the fact that the proposed treatment is usually well tolerated, or else getting the patient’s permission to inform less than fully about its possible side effects.”

Two authors disclosed financial ties to the pharmaceutical industry.

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