Assessing expectancy and suggestibility in a trial of escitalopram v. psilocybin for depression
Psychological Medicine – January 22, 2024
Source: OpenAlex
Summary
Surprisingly, psilocybin's therapeutic effect for major depressive disorder may be less influenced by patient expectations than escitalopram, a common antidepressant. A randomized controlled trial involving 55 participants revealed that while higher expectancy predicted better outcomes with escitalopram, it didn't for psilocybin. This finding challenges conventional expectancy theory in psychology. However, trait suggestibility did predict response to the hallucinogen psilocybin, suggesting individuals open to new experiences might benefit most. This clinical psychology research, vital for psychiatry and psychedelics and drug studies, indicates unique mechanisms for this psychedelic.
Abstract
Abstract Background To investigate the association between pre-trial expectancy, suggestibility, and response to treatment in a trial of escitalopram and investigational drug, COMP360, psilocybin, in the treatment of major depressive disorder (ClinicalTrials.gov registration: NCT03429075). Methods We used data ( n = 55) from our recent double-blind, parallel-group, randomized head-to-head comparison trial of escitalopram and investigational drug, COMP360, psilocybin. Mixed linear models were used to investigate the association between pre-treatment efficacy-related expectations, as well as baseline trait suggestibility and absorption, and therapeutic response to both escitalopram and COMP360 psilocybin. Results Patients had significantly higher expectancy for psilocybin relative to escitalopram; however, expectancy for escitalopram was associated with improved therapeutic outcomes to escitalopram, expectancy for psilocybin was not predictive of response to psilocybin. Separately, we found that pre-treatment trait suggestibility was associated with therapeutic response in the psilocybin arm, but not in the escitalopram arm. Conclusions Overall, our results suggest that psychedelic therapy may be less vulnerable to expectancy biases than previously suspected. The relationship between baseline trait suggestibility and response to psilocybin therapy implies that highly suggestible individuals may be primed for response to this treatment.