Who believes psychedelic-assisted therapies work? Risky cannabis use and other factors are associated with positive treatment-outcome expectancies

Introduction: Treatment-outcome expectancies are an individual’s beliefs about how a medical or psychological intervention will affect them and others. These response expectancies represent serious potential confounds to clinical trials of psychedelic-assisted therapies for a variety of conditions because of difficulties associated with blinding psychedelic trials. On the other hand, expectancies also represent opportunities for practitioners to promote desired clinical outcomes. Therefore, a stronger understanding of factors associated with positive treatment-outcome expectancies for psychedelics could be useful to both scientists and clinicians. Method: The present study examined treatment-outcome expectancies for psychedelic-assisted therapies with psilocybin or lysergic acid diethylamide (LSD) among undergraduates (73% female, 81% White, 30% Hispanic, and 22% psychedelic-experienced; Mage = 19.95 years, median = 19.0, SD = 3.14). A generalized linear mixed model (GLMM) was used to test the hypothesis that riskier alcohol, cannabis, and other substance use would be associated with more positive treatment-outcome expectancies. Results: Consistent with our hypothesis, riskier cannabis use was significantly associated with more positive expectancies. However, neither riskier drinking nor other drug use were significant predictors. Prior engagement with psychedelic-related media and exposure to other peoples’ psychedelic experiences also predicted treatment-outcome expectancies. Conclusion: Individuals with riskier cannabis use may hold stronger beliefs in the transdiagnostic effectiveness of psychedelic-assisted therapies. This suggests that clinical trials of psychedelic-assisted interventions for cannabis use disorder may be particularly vulnerable to expectancy-related confounds. Psychedelic-therapy practitioners treating patients with risky cannabis use may consider patients’ beliefs in the effectiveness of psychedelics when discussing treatment options and delivering psychedelic interventions.