Cited by 109Psychedelics and Drug StudiesSchizophrenia research and treatmentHallucinations in medical conditions

Double-blind comparison of the two hallucinogens psilocybin and dextromethorphan: effects on cognition

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Barrett, Frederick S., Carbonaro, Theresa M., Hurwitz, Ethan, Johnson, Matthew W., Griffiths, Roland R.·2018·Psychopharmacology

Abstract

Objectives Classic psychedelics (serotonin 2A receptor agonists) and dissociative hallucinogens (NMDA receptor antagonists), though differing in pharmacology, may share neuropsychological effects. These drugs, however, have undergone limited direct comparison. This report presents data from a double-blind, placebo-controlled within-subjects study comparing the neuropsychological effects of multiple doses of the classic psychedelic psilocybin with the effects of a single high dose of the dissociative hallucinogen dextromethorphan (DXM).Methods Twenty hallucinogen users (11 females) completed neurocognitive assessments during five blinded drug administration sessions (10, 20, and 30 mg/70 kg psilocybin; 400 mg/70 kg DXM; and placebo) in which participants and study staff were informed that a large range of possible drug conditions may have been administered.Results Global cognitive impairment, assessed using the Mini-Mental State Examination during peak drug effects, was not observed with psilocybin or DXM. Orderly and dose-dependent effects of psilocybin were observed on psychomotor performance, working memory, episodic memory, associative learning, and visual perception. Effects of DXM on psychomotor performance, visual perception, and associative learning were in the range of effects of a moderate to high dose (20 to 30 mg/70 kg) of psilocybin.Conclusions This was the first study of the dose effects of psilocybin on a large battery of neurocognitive assessments. Evidence of delirium or global cognitive impairment was not observed with either psilocybin or DXM. Psilocybin had greater effects than DXM on working memory. DXM had greater effects than all psilocybin doses on balance, episodic memory, response inhibition, and executive control.

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  • Single doses of cannabis cause deficits in decision making and working memory.

    “Single doses of cannabis have been found to cause deficits in decision making and working memory (7 -9)”

    From Hazy memories in the courtroom: A review of alcohol and other drug effects on false memory and suggestibility (2021) · cites this paper as [8]

    The Discussion section on executive function reports working-memory effects of psilocybin and dextromethorphan, not cannabis. Searches for cannabis, THC, single-dose effects, and decision making found no passage addressing the attributed claim; page numbers were unavailable in our copy. (LLM, conf=0.76)

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  • Cognitive impairment is most prominent during 2 h after smoking, but may be detectable up to 4 to 6 h after smoking.

    “Cognitive impairment is most prominent during 2 h after smoking, but may be detectable up to 4 to 6 h after smoking (8, 30).”

    From Hazy memories in the courtroom: A review of alcohol and other drug effects on false memory and suggestibility (2021) · cites this paper as [8]

    The Methods and Materials > Procedures section describes psilocybin and dextromethorphan administered in capsules, not smoked substances. The Discussion addresses cognitive effects after capsule administration but does not establish that impairment is greatest in the first two hours after smoking or remains detectable four to six hours afterward. Searches for those smoking-related time windows found no supporting passage in our copy. (LLM, conf=0.78)

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Authors
Barrett, F. S., Carbonaro, T. M., Hurwitz, E., Johnson, M. W., & Griffiths, R. R.
Affiliations
Johns Hopkins University (US)
Corresponding author
Barrett, Frederick S.
Venue
Psychopharmacology
Published
2018-07-30
Volume
235
Issue
10
Pages
2915-2927
ISSN
  • 0033-3158 (ISSN-L)
  • 1432-2072
OpenAlex
W2886435130
Cited by
109
References
78
Citations by year
2026: 14 · 2025: 11 · 2024: 23 · 2023: 19 · 2022: 18 · 2021: 18 · 2020: 5 · 2019: 1
FWCI
7.05
Type
journal article
Language
en
Open access
Locations
  • Psychopharmacology (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
National Institute on Drug Abuse (R01DA03889, T32DA007209, R03DA042336, R01DA035277)
Topics
  • Social Sciences › Psychology › Clinical Psychology › Psychedelics and Drug Studies
  • Health Sciences › Medicine › Psychiatry and Mental health › Schizophrenia research and treatment
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Hallucinations in medical conditions
Keywords
psilocybin, dextromethorphan, hallucinogens, classic psychedelics, cognitive effects, dose-response relationship, working memory, episodic memory, associative learning, psychomotor performance, visual perception, response inhibition, executive function, balance, delirium, neuropsychological assessment
MeSH terms
Adult, Association Learning, Cognition, Dextromethorphan, Dose-Response Relationship, Drug, Double-Blind Method, Female, Hallucinogens, Humans, Male, Memory, Short-Term, Psilocybin, Psychomotor Performance, Visual Perception, Young Adult

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