Optimizing Expectations Leads to Enhanced Efficacy of a Mindfulness-Based Intervention in Individuals With Low-Baseline Expectations: A Randomized Controlled Trial.

INTRODUCTION: Treatment expectations for medical and psychological treatments and positive patient-provider interactions are critical mechanisms driving the placebo effect and may augment an intervention's effects. However, it remains unclear whether optimizing treatment expectations is beneficial for all individuals. This pilot randomized controlled trial (three-arm parallel design) examined whether i) optimizing treatment expectations would augment the efficacy of a mindfulness intervention and ii) whether participants' treatment expectations at baseline would moderate these effects.

METHODS: Sixty-six healthy participants were randomized (1:1:1) to one of 3 experimental groups: i) body scan and an instruction aiming to optimize treatment expectations (EXPECT), ii) body scan and a neutral instruction (NEUTRAL), or iii) listening to an audiobook and neutral instruction (CONTROL). Primary outcomes were changes in positive and negative affect; secondary outcomes included treatment expectations, perceived stress, and mindfulness. Baseline expectations were assessed as a moderator using ANCOVA.

RESULTS: ANCOVA indicated a group effect on positive affect (p = 0.018, d = 0.65), with individuals in the EXPECT group showing a stronger reduction than both other groups. Post-hoc comparisons showed significant differences between EXPECT and NEUTRAL (p = 0.015, d = -0.77) and between EXPECT and CONTROL (p = 0.012, d = -0.80). Analyzes did not indicate main effects on other outcomes. Participants with low baseline expectations showed a stronger increase in reported treatment expectations and mindfulness, as well as a more pronounced decrease in perceived stress from baseline- to post-assessment in the EXPECT group compared to both other groups. In contrast, individuals with high baseline expectations indicated less stress reduction when undergoing the body scan and receiving the instruction with positive expectation induction (EXPECT) compared to the group with a body scan and neutral instruction (NEUTRAL).

CONCLUSION: Inducing positive treatment expectations may be beneficial for individuals with low baseline expectations, likely due to an enhanced placebo response. However, it may be counterproductive for individuals with high baseline outcome expectations and could reflect expectation violation effects.