The role of treatment beliefs in the placebo effect

• Main Author: Watkinson, Andrew
• Published: University College London (University of London) 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.756102

Treatment beliefs and related illness representations are important determinants of treatment uptake and adherence. This thesis explores whether these representations might also explain placebo effects. Within this thesis, a literature review outlines placebo mechanisms and summarises theory and research in relation to representations of treatment and illness. The empirical section that follows addresses three research questions identified by the review and explored in four studies. Study 1 was a randomised controlled trial using the cold pressor paradigm in healthy volunteers (n=167). This demonstrated that treatment beliefs predicted pain responses to two placebos described as pharmaceutical versus natural, consistent with the theoretical model of specific and general treatment beliefs. Study 2 involved patients (n=136) with symptoms of gastric-reflux, undergoing a diagnostic test. It showed that pain intensity, in response to oesophageal saline perfusion, could be significantly reduced by describing the saline as ‘therapeutic’ rather than as a ‘non-therapeutic’ component of the test procedure. Patients’ beliefs about their condition moderated the effect of framing on pain response to saline with more negative representations of gastric-reflux associated with lower therapeutic response. Studies 3 and 4 were conducted in parallel to explore whether placebo-related treatment beliefs could be modified by brief interventions designed to change beliefs. Study 3, an analogue study in health volunteers (n=222), found that a brief informational intervention designed to increase coherence between representations of asthma and its treatment did not influence treatment beliefs. In Study 4, placebo effects to cough induction in health volunteers (n= 62) were influenced by treatment beliefs (general pharmaceutical schema), but treatment beliefs were again, not influenced by the intervention used in Study 3. Despite their limitations the empirical studies suggest that treatment beliefs and illness representations are related to placebo effects, justifying further work to extend the scope and quality of this research.