Prescribing Placebos: An Experimental Examination of the Role of Dose, Expectancies, and Adherence in Open-Label Placebo Effects

Background: Recent evidence indicates that placebo effects can occur even when patients know that they are taking a placebo, termed the open-label placebo effect. Aim: To assess whether placebo dose (1 pill per day versus 4 pills per day), treatment expectancies, and adherence contribute to open-label placebo effects. Method: Healthy undergraduate participants were randomly assigned to take 1 or 4 open-label placebo pills per day, or to a no treatment control group. Placebo-treated participants took a 5-day course of an open-label placebo described as enhancing physical (symptoms and sleep) and psychological (positive and negative emotional experience) wellbeing. Expectancies about placebo effectiveness and wellbeing were assessed at baseline, and wellbeing and adherence were assessed after the 5-day course of treatment. Results: Medium to large open-label placebo effects were evidenced in all wellbeing outcomes including sleep quality. Dose did not influence these effects. Both treatment expectancies and adherence were significant independent predictors of enhanced wellbeing in the two psychological wellbeing outcomes and the experience of physical symptoms but sleep quality improved independently. Conclusions: This the first study to demonstrate the effect of open-label placebos in improving wellbeing and sleep quality, and to show that open-label placebo reposes do not appear to be dose-dependent, but for most wellbeing outcomes are independently predicted by both positive expectancies and treatment adherence