Interaction between disgust proneness and perception of treatment efficacy predicts response to a disgust placebo.

Placebo responsiveness is highly variable across individuals and has been shown to be difficult to predict solely based on personality traits. The present study examined the interaction between a specific trait and state variable (disgust proneness and perceived effectiveness of a disgust placebo) on placebo responsiveness. We presented 145 participants with an inert pill, which was introduced as an effective anti-nausea drug. Disgust responses were elicited by a validated picture set, which was viewed once with and once without the disgust placebo. The results showed that the placebo was effective in reducing experienced disgust. When predicting placebo responsiveness, the results showed a significant interaction between perceived treatment effectiveness and disgust proneness. Specifically, effectiveness ratings were a significant predictor of placebo response only for individuals high in disgust proneness. The results suggest that the joint consideration of specific state and trait factors can be used to optimize placebo responsiveness.