Personality and placebo responses in non-pain paradigms: Building a Transactional Model of Placebo Responding

Abstract

In a modern healthcare environment burdened by symptomatic and mental-health related ailments, the placebo effect may represent a useful clinical tool. However, with the bulk of research to date conducted in pain contexts, more exploration is needed into the power of the placebo in other settings. Similarly, insights into the type of person most likely to respond to placebo treatments arise predominantly from pain contexts, and it is not known whether the same personalities are responsive in non-pain settings. This research programme aimed to address these two limitations in the extant literature by investigating: (1) What are the capabilities of placebo suggestion outside the context of pain; and (2) Which personality characteristics predict placebo responses in these other contexts. After a systematic review of the placebo personality literature, three experimental studies were conducted to investigate placebo effects in the context of: (1) acute psychosocial stress recovery (N = 60); (2) histamine-induced inflammatory skin reactions (N = 48); and (3) a take-home placebo treatment for stress, anxiety, and depressive symptoms arising from the demands and challenges of everyday life (N = 77). All three studies employed suggestive placebo protocols and used physically healthy samples. Results extend findings from prior investigations and offer several novel, incremental findings to the extant placebo literature. Suggestive placebo protocols were shown to enhance physiological recovery from acute psychosocial stress; to reduce the experience of itch; and to ameliorate symptoms of stress, anxiety and depressive symptoms in a naturalistic setting. In answering the second research question, the Transactional Model of Placebo Responding (TMPR) was developed to provide a framework for understanding how personality traits might interact with environmental cues to influence placebo responses. Specifically, the model proposes that there are two facets of responsiveness - inward orientation and outward orientation - which may respond to different environmental cues. The findings from this research programme offer both empirical and theoretical contributions to the placebo literature. More research is needed to replicate and extend results; however, once properly refined and tested, the TMPR may offer utility in predicting who might be responsive to placebo treatments, thus maximising the placebo’s potential as a clinical tool.