Experimental Assessment of Nocebo Effects and Nocebo Side Effects: Definitions, Study Design, and Implications for Psychiatry and Beyond

Interest in nocebo effects is increasing exponentially: a Google Scholar search for articles referencing nocebo in 1998 (20 years ago) yields 90 results, increasing to 449 in 2008 (10 years ago) and to 1600 in 2018.Increased attention has likely resulted from recognition of the prevalence and potential seriousness of nocebo effects in clinical contexts.It is estimated that up to 97% of reported pharmaceutical side effects are not caused by the drug itself but rather by nocebo effects and symptom misattribution (1).These nocebo effects can cause symptoms serious enough to require hospitalization and medical intervention (2).As a result of the increased recognition of the importance of nocebo effects, experimental research seeking to understand how nocebo effects are formed has also intensified.As the literature on nocebo effects has expanded, additional methodological decision points arise for researchers in this area.In this article, we discuss a set of methodological issues that result from emerging approaches to studying nocebo effects, including distinctions between designs for standard nocebo effects versus nocebo side effects, the information provided by selecting different types of control groups in experimental designs, and the distinction between "true" nocebo effects and symptom misattribution.This discussion will focus on between-subjects designs, using examples of nocebo effects that are generated by verbal/written transmission of information.For each issue, we compare the different methodologies and seek to highlight the strengths and limitations of these approaches. NOCEBO EFFECTS AND NOCEBO SIDE EFFECTS DESIGNS: DEFINITIONSDefinitions of the nocebo effect typically focus on the role of negative expectations in producing aversive outcomes [e.g.,].In contrast, Faasse (8) extends this definition to incorporate past experience and other aspects of the treatment context.We would refine this further to define nocebo effects as unpleasant or adverse outcomes triggered by the treatment context, beyond any inherent pharmacological effects of the treatment itself.These nocebo effects are scientifically measurable effects caused by psychological processes including negative expectations, classical conditioning, and observational learning (9).Although not always differentiated, there are two variants of nocebo effects that researchers examine: primary nocebo effects and nocebo side effects.Experimental designs that study primary

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