The Influence of Choice on Placebo and Nocebo Responding

Abstract

Expectations have previously been used to produce both positive placebo outcomes as well as negative or harmful nocebo outcomes. Recent placebo research has also demonstrated that giving participants a choice over the placebo they take can actually enhance the placebo response. However, the effect of choice on nocebo outcomes has not been studied. This study aimed to investigate the placebo and nocebo response in participants who were either able or unable to choose their placebo medication. Desire for control level was also measured to test whether desire for control could influence the impact of choice. Using the cover story of beta blockers being investigated for exam anxiety, 60 university students completed a laboratory session at a clinical centre, and completed a follow up assessment the next day. Two equally valued beta blockers, different in three minor aspects, were presented, and participants were required to express their preference. Participants were then randomised to choose or not choose. If participants were not able to choose, they were randomly assigned a beta blocker to take. The results revealed greater medication effectiveness – in terms of diastolic blood pressure and heart rate – in the choice group, and increased medication side effects in the no choice group at follow up. Medication effectiveness was demonstrated by a heart rate interaction effect (p = .048), wherein heart rate in the choice group decreased over the session and heart rate in the no choice group increased over the session. Medication effectiveness was also demonstrated by a significant increase in diastolic blood pressure over the session in the no choice group (p = .011), that was not present in the choice group. Side effect reporting did not significantly differ between the choice and no choice group on the day of the session, however, the following day there were significantly more side effects reported in the no choice group compared to the choice group (p = .010). The results were not simply due to the choice group receiving their preferred medication, as subgroup analyses showed no differences in medication effectiveness, or symptoms and side effects between participants who did and did not receive their preferred medication. There was a desire for control effect, where participants that were assigned to the condition that matched their desire for control level (e.g. high desire for control being assigned to choice condition) experienced greater medication effectiveness, in terms of heart rate (ps = .030 - .046), and fewer medication side effects at follow up (p = .016). The findings of the current study demonstrate that individuals who are able to choose their treatment, compared to those unable to choose, experience greater medication effectiveness and fewer side effects. These findings hold clinical implications in terms of medication funding and prescribing.