The association between personality traits and placebo effects: A preregistered systematic review and meta-analysis

Placebo effects are ubiquitous yet highly variable between individuals, and therefore strongly impact clinical trial outcomes. It is unclear whether dispositional psychological traits influence responsiveness to placebo. This preregistered meta-analysis and systematic review synthesized the literature investigating the association between personality traits and placebo effects. Based on 19 studies with 712 participants, we performed formal meta-analyses for 10 different personality traits. We did not find evidence of associations between any of these traits and magnitude of placebo effects, which was supported by equivalence tests. Furthermore, we did not find evidence for moderating factors such as placebo manipulation type (Conditioning, non-conditioning) or condition (pain, non-pain). However, the current synthesis was not statistically powered for full inquiry into potential conditional or interactive associations between personality and situational variables. These findings challenge the notion that personality influences responsiveness to placebos and contradict its utility for identifying placebo “responders” and “non-responders”.