Causes, Mechanisms, and Mitigation of Socially-Induced Nocebo Effects

Abstract

The nocebo effect refers to adverse symptoms that arise in response to treatment but cannot be explained by its active properties. Despite their major clinical, social, and economic burden, nocebo effects remain understudied. Social learning, where people learn by observing or interacting with others, is a potent pathway for nocebo effects. In healthcare, where treatment experiences can be shared face-to-face and through mainstream and social media, understanding socially-acquired nocebo effects matters. This thesis examined the causes, mechanisms, spread, and reduction of socially-induced nocebo effects. Chapter 1 introduces nocebo effects, induction pathways, and key mechanisms. Chapter 2 presents a review and meta-analysis showing that observing adverse symptoms in another person produces medium-to-large nocebo effects compared with no treatment, with effects similar to classical conditioning and larger than explicit instruction. Prior studies, however, only tested cases where model and observer had identical experiences. Chapters 3 and 4 tested whether nocebo effects arise when the model’s experience differs from the observer’s. Using a virtual reality model of cybersickness and a simulated clinical paradigm, these studies showed that social nocebo effects generalise to similar treatments and contexts. This suggests social expectations are not limited to the modelled intervention, widening the scope of harm. Chapters 3 and 5 tested ways to reduce social nocebo effects. Choice was not found to reduce socially elicited cybersickness. In contrast, positive social modelling, where side effect warnings were paired with a peer reporting no side effects, reduced symptom severity. This gives initial evidence that social learning can also counter nocebo formation. Overall, this thesis advances understanding of socially-induced nocebo effects and shows that continued work is needed to develop and test ways to reduce their burden on individuals and the wider community.