Psychedelic research faces unique methodological challenges beyond those typical of psychotherapy and pharmacology trials. The pronounced subjective effects of high-dose psychedelics make it difficult to mask participants to their treatment condition. Positive media coverage inflates participants' expectations for benefit, and unmasking combined with expectations can produce large placebo and nocebo effects. Recommendations to improve masking and reduce expectancy bias include careful study development, participant recruitment and selection, incomplete disclosure of study design, choice of active placebo, and measurement of expectations and masking efficacy. Incorporating these design elements aims to reduce bias and improve the ability to discern treatment-specific effects.
Clinical trials of psychedelic therapy face unique methodological challenges that threaten the interpretability of results. The intense subjective effects of high-dose psychedelics make it difficult to mask participants to their treatment condition, and widespread positive media coverage inflates participants' expectations for benefit. Participant unmasking and treatment expectations can interact, making psychedelic therapy highly susceptible to large placebo and nocebo effects. Recommendations to improve rigor include careful study development, participant recruitment and selection, incomplete disclosure of the study design, choice of active placebo condition, and measurement of participant expectations and masking efficacy. Incorporating these design elements is intended to reduce bias and increase the ability to discern treatment-specific effects.