The influence of choice on placebo and nocebo effects

Abstract

Given the ubiquity of the placebo effect and its counterpart, the nocebo effect, in clinical settings, an important question is if and how we can harness the placebo and nocebo effects to improve health outcomes. A growing body of research suggests that choice may facilitate the placebo effect and reduce nocebo side effects. The aim of this project was to better understand the impact of choice on placebo and nocebo effects. This involved a systematic review and meta-analysis of the influence of choice on the placebo effect and four experimental studies exploring the role of choice in various placebo and nocebo contexts using experimentally-induced pain. The meta-analysis identified 15 studies whereby choice was found to have a small-to-moderate overall effect on enhancing the placebo effect, but interestingly this effect was inversely proportional to the size of the placebo effect without choice, suggesting that choice may be more beneficial in weaker placebo contexts. The first experimental study extended on this and showed that choice facilitated placebo hypoalgesia more effectively in weaker placebo contexts, in this case conditioning with partial reinforcement. Study 2 found that providing choice also enhanced the size of open-label placebo hypoalgesia. The final two studies examined the choice effect on conditioned nocebo hyperalgesia. Surprisingly, Study 3 found that choice increased, rather than decreased nocebo hyperalgesia. Study 4 thus tested whether providing information about the benefit of choice would counteract the extent to which choice augmented nocebo hyperalgesia, but this was found to be ineffective. Taken together, these findings suggest choice may be a useful method for boosting treatment outcomes via enhancing the placebo effect. Yet, at the same time, caution must be taken when offering individuals choice in any clinical or applied scenarios where conditioned nocebo hyperalgesia could be induced because choice also increased this effect.