Double-blind comparison of the two hallucinogens psilocybin and dextromethorphan: similarities and differences in subjective experiences
This double-blind, placebo-controlled study (n=20) with psilocybin (10, 20, 30mg/70kg) and DMX (400mg/70kg) finds very similar subjective effects between the two drugs. The visual, mystical, and insightful effects were more pronounced with psilocybin, disembodiment with DMX.
Authors
- Matthew Johnson
- Theresa Carbonaro
Published
Abstract
Rationale
Although psilocybin and dextromethorphan (DXM) are hallucinogens, they have different receptor mechanisms of action and have not been directly compared.
Objective
This study compared subjective, behavioral, and physiological effects of psilocybin and dextromethorphan under conditions that minimized expectancy effects.
Methods
Single, acute oral doses of psilocybin (10, 20, 30 mg/70 kg), DXM (400 mg/70 kg), and placebo were administered under double-blind conditions to 20 healthy participants with histories of hallucinogen use. Instructions to participants and staff minimized expectancy effects. Various subjective, behavioral, and physiological effects were assessed after drug administration.
Results
High doses of both drugs produced similar increases in participant ratings of peak overall drug effect strength, with similar times to maximal effect and time-course. Psilocybin produced orderly dose-related increases on most participants rated subjective measures previously shown sensitive to hallucinogens. DXM produced increases on most of these same measures. However, the high dose of psilocybin produced significantly greater and more diverse visual effects than DXM including greater movement and more frequent, brighter, distinctive, and complex (including textured and kaleidoscopic) images and visions. Compared to DXM, psilocybin also produced significantly greater mystical-type and psychologically insightful experiences and greater absorption in music. In contrast, DXM produced larger effects than psilocybin on measures of disembodiment, nausea/emesis, and light-headedness. Both drugs increased systolic blood pressure, heart rate, and pupil dilation and decreased psychomotor performance and balance.
Conclusions
Psilocybin and DXM produced similar profiles of subjective experiences, with psilocybin producing relatively greater visual, mystical-type, insightful, and musical experiences, and DXM producing greater disembodiment.
Research Summary of 'Double-blind comparison of the two hallucinogens psilocybin and dextromethorphan: similarities and differences in subjective experiences'
Introduction
Classic serotonergic psychedelics (serotonin 2A receptor agonists) such as psilocybin and dissociative hallucinogens (NMDA receptor antagonists) such as dextromethorphan (DXM) differ in primary pharmacology but may produce overlapping subjective effects. Earlier blinded work had found that a high oral dose of DXM (400 mg/70 kg) produced subjective profiles similar to those of classic hallucinogens on a range of self-report measures, yet relatively little work has directly compared the acute neurocognitive effects of classic and dissociative hallucinogens in the same participants. Barrett and colleagues designed a double-blind, placebo-controlled, within-subjects complete-crossover study to compare dose-dependent neurocognitive effects of oral psilocybin (10, 20, and 30 mg/70 kg) with a single high oral dose of DXM (400 mg/70 kg). The investigators tested two primary hypotheses: that DXM would produce greater impairments than psilocybin on psychomotor, memory, and executive-function tasks, and that psilocybin would produce greater effects on a visual-perception task given its known visual network effects.
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Study Details
- Study Typeindividual
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- Compounds
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- APA Citation
Carbonaro, T. M., Johnson, M. W., Hurwitz, E., & Griffiths, R. R. (2018). Double-blind comparison of the two hallucinogens psilocybin and dextromethorphan: similarities and differences in subjective experiences. Psychopharmacology, 235(2), 521-534. https://doi.org/10.1007/s00213-017-4769-4
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