Is it personality or genes? - A secondary analysis on a randomized controlled trial investigating responsiveness to placebo analgesia

OBJECTIVES: To understand how different individuals respond to placebo effects, it is relevant to disentangle the influence of someone's personality and genetic variations. The aim of this exploratory study was to investigate the role of different personality characteristics and different single-nucleotide polymorphisms (SNPs) on the responsiveness to placebo analgesia. METHODS: Secondary data analyses were conducted on an experimental behavioural study in healthy controls primarily aimed at the influence of three learning mechanisms (i.e., verbal suggestions, classical conditioning, or observational learning) or combinations thereof, on placebo analgesia in heat pain. Moderation by five different personality characteristics (optimism, neuroticism, worrying, empathy, and somatosensory amplification) was studied. Also, the predictive role of three different SNPs on the OPRM-1 gene, the COMT gene, and the FAAH gene on placebo analgesia was assessed. The personality characteristics were studied with validated questionnaires. The genetic variants were obtained by sequencing DNA from saliva cells. RESULTS: The moderation analysis from 206 participants concerning the personality characteristics did not show significant effects. Of the 108 (52%) genotyped participants, the results showed no significant relationship between any of the SNPs and placebo analgesia. CONCLUSIONS: Results did not support a role of a person's personality characteristics or genetic variations in predicting their responsiveness to placebo analgesia through learning mechanisms. The clinical relevance of predicting someone's responsiveness to placebo effects, therefore, requires careful reconsideration.