Randomized trial demonstrates open-label placebos reduce distress and hair cortisol in students, indicating non-deceptive treatments mitigate real-world psychophysiological stress.
Key Points
To evaluate the effect of a 4-week open-label placebo intervention on psychological distress and hair cortisol concentrations during exam stress, and to examine whether dispositional optimism moderates these responses.
Conducted a randomized controlled trial in 202 healthy university students preparing for mandatory oral examinations, randomized to either an open-label placebo (OLP) group or a control group for 4 weeks.
Measured psychological distress across repeated assessments of negative affect, test anxiety, and subjective stress, alongside hair cortisol concentrations (HCC) before and during the intervention.
Assessed dispositional optimism and treatment expectations to evaluate their individual and interactive moderating effects on psychological and physiological outcomes.
Open-label placebos significantly reduced both psychological distress and hair cortisol concentrations compared with the control group.
Dispositional optimism significantly moderated the OLP effect on hair cortisol concentrations, with less optimistic participants showing the greatest reductions in cortisol independent of expectation.
Optimism did not directly moderate OLP effects on psychological distress alone, but distress outcomes were significantly influenced by a three-way interaction between group, optimism, and treatment expectation.