The role of expectations and tailored feedback on the open-label Placebo effect.

Open label placebos (OLPs) refer to the non-deceptive administration of inert treatment. This pre-registered study (AsPrediced#139837) explored the role of expectations and tailored health feedback on the OLP effect using an automated online procedure. Healthy participants (N = 293) were randomised to a 10-day course of OLP pills with veridical feedback (OLP-Feedback: N = 92), without feedback (OLP-Standard: N = 105), or to a no-treatment control (NTC: N = 96). Participants were informed the pills were inert but may enhance wellbeing. Wellbeing was assessed at baseline, day-5 and day-10. Feedback was delivered on day-5 and day-10 via interactive graphs and descriptive statistics. OLP-treatment significantly improved wellbeing (negative emotions and sleep quality), while feedback did not significantly enhance this effect. Expectations for improvement were significantly elevated among OLP-treated participants across the 10-day study. However, at the individual level, expectations only mediated OLP outcomes once treatment experience had been acquired. Results reconcile inconsistencies in the literature regarding mechanisms.