'Oxytocin' for the outwardly oriented: Evidence for interactive effects in placebo responding

In order to harness the placebo effect for clinical benefit, more research is needed to determine who might be responsive to a placebo treatment. Recently, a two-faceted Transactional Model of Placebo Responding (TMPR) was offered, which suggests different personality types might respond to different contextual cues. The current study directly tested this model by manipulating treatment descriptors to match the two purported facets of responsiveness.

Physically healthy volunteers (N=77) experiencing life stress were randomised to either the: (1) wait-list control, (2) 'serotonin treatment' group; or (3) 'oxytocin treatment' group. Both treatment groups received an 'antistress' intranasal spray (placebo). The 'serotonin' and 'oxytocin' treatments were described to appeal to the two purported facets responsiveness set out in the TMPR, inward and outward orientation. The BIS/BAS scale was used as proxies for inward (BIS) and outward (BAS) orientation. It was hypothesised that high BAS types would be more responsive to the 'oxytocin' and high BIS types would be more responsive to the 'serotonin'.

Findings provide partial support for hypotheses, with high but not low BAS types having a greater response to the 'oxytocin' placebo; but the pattern of responses from high BIS types were contrary to predictions.

Findings indicate interactions between personality type and environmental cues may contribute to placebo responding, but more research is needed to investigate possible operationalisations of responsiveness and the contextual cues to which different types may respond.