Open-label placebo reduced stress hormones and distress in exam-stressed students
A randomized trial of 202 university students found that openly-disclosed placebo treatment over 4 weeks significantly lowered both psychological distress and hair cortisol (a stress hormone marker), with effects strongest in less optimistic individuals.
Researchers randomly assigned 202 healthy university students preparing for mandatory oral exams to either a 4-week open-label placebo (OLP) intervention or a control group. Open-label placebos are treatments given with full disclosure that they are placebos, which paradoxically can still produce benefits.
Psychological distress was measured repeatedly through negative affect, test anxiety, and subjective stress; hair cortisol concentrations (HCC), a marker of chronic stress, were measured before and after the intervention. Results showed OLP significantly reduced psychological distress compared to controls, and also meaningfully lowered hair cortisol concentrations. Interestingly, dispositional optimism—whether individuals tend to expect positive outcomes—moderated the effect on hair cortisol: less optimistic students showed the strongest reductions in cortisol, independent of their treatment expectations. Optimism did not moderate the psychological distress benefits, but the effect on distress did depend on a three-way interaction of group assignment, optimism level, and treatment expectations. One limitation is that the study involved only healthy university students in a specific stressor context (exam preparation), so findings may not generalize to other populations or chronic stress settings.
The study adds mechanistic detail to how placebos work: physiological responses (cortisol suppression) and psychological responses (distress reduction) appear to operate via different pathways. The cortisol effect was strongest in individuals low in dispositional optimism, suggesting that those naturally less inclined to expect good outcomes may benefit most from an explicit, structured intervention—even when told it is a placebo. This hints that expectancy and trait optimism interact differently depending on whether the outcome is hormonal or subjective. The exam context is ecologically valid but acute; chronic stress studies would strengthen claims. Hair cortisol integrates weeks of exposure, making it a more robust biomarker than single-point saliva samples, though cortisol is one of many stress physiology markers and does not capture the full picture of stress biology.
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Open in Cadence →References
- Dispositional optimism and open-label placebo responses in hair cortisol concentrations and psychological distress-A randomized controlled trial. — Applied psychology. Health and well-being (Read the original)