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Peer-reviewedCC BY 4.0Journal of Psychopharmacology (Oxford, England)

Defining ‘psychedelic’

  • A. E. Ostrand1
  • M. M. Nour2,3
  • C. Timmermann4,5
  • A. Rosati1,6
  • L. X. Luan5,7
  • A. Gomez-Emilsson8
  • J. Bornemann5
  • K. T. Greenway9,10
  • L. Roseman7
  • Carhart-Harris R1,11
11 affiliations
  1. 1Carhart-Harris Lab, Department of Neurology, University of California San Francisco, USA
  2. 2Department of Psychiatry, University of Oxford, UK
  3. 3Max Planck UCL Centre for Computational Psychiatry and Ageing Research, London, UK
  4. 4UCL Centre for Consciousness Research, Department of Experimental Psychology, University College London, UK
  5. 5Centre for Psychedelic Research, Department of Brain Sciences, Imperial College London, UK
  6. 6Department of Psychiatry and Behavioral Sciences, University of California San Francisco, USA
  7. 7Department of Psychology, University of Exeter, UK
  8. 8Qualia Research Institute, San Francisco, CA, USA
  9. 9Lady Davis Institute, Jewish General Hospital, Montréal, QC, Canada
  10. 10Department of Psychiatry, Faculty of Medicine, McGill University, Montréal, QC, Canada
  11. 11Centre for Psychedelic Research, Division of Psychiatry, Department of Brain Sciences, Imperial College London, UK
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Abstract

Humphry Osmond coined the term ‘psychedelic’ in 1956, conjoining ‘psyche’ for ‘soul’ and ‘delic’ for ‘to manifest’ or ‘illuminate’. Soul-illumination is a compound noun that describes a psychological state or process. Osmond intended for it to be a taxonomic noun—naming, not just a state—but a category of drug that can induce this psychological effect as its principal action. Consistent with the etymology of psychedelic, the present work respects the fundamental importance of phenomenology. Accordingly, we examine the main subjective effect of three different psychoactive drugs, psilocybin, ketamine, and MDMA (3,4-methylenedioxymethamphetamine) (variable label, Drug). Over 200 participants rated Delphi-generated subjective rating scale items based on their personal experiences with all 3 drugs. Factor analyses revealed three or four sufficiently independent dimensions of subjective experience (variable label, Effects). A machine-learning classifier successfully predicted Drug from Effects, validating the hypothesis that psilocybin, ketamine and MDMA have categorically distinct subjective effect profiles, differentiable by (1) visions and psychological insight (psilocybin), (2) dissociation (ketamine) and (3) pro-social and loving feelings (MDMA). We conclude that psilocybin is an exemplar psychedelic—a category of drug definable by the induction of a psychedelic state. The quintessential psychedelic phenomenon is a subjective state characterized by visions and psychological insight.

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Cite

BibTeXRIS
BibTeX
@article{ostrand2026defining,
  title = {{Defining ‘psychedelic’}},
  author = {A. E. Ostrand and M. M. Nour and C. Timmermann and A. Rosati and L. X. Luan and A. Gomez-Emilsson and J. Bornemann and K. T. Greenway and L. Roseman and Carhart-Harris R},
  journal = {Journal of Psychopharmacology (Oxford, England)},
  year = {2026},
  month = aug,
  doi = {10.1177/02698811261464986},
  url = {https://doi.org/10.1177/02698811261464986},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Defining ‘psychedelic’
AU  - A. E. Ostrand
AU  - M. M. Nour
AU  - C. Timmermann
AU  - A. Rosati
AU  - L. X. Luan
AU  - A. Gomez-Emilsson
AU  - J. Bornemann
AU  - K. T. Greenway
AU  - L. Roseman
AU  - Carhart-Harris R
PY  - 2026
DA  - 2026/08/17
JO  - Journal of Psychopharmacology (Oxford, England)
DO  - 10.1177/02698811261464986
UR  - https://doi.org/10.1177/02698811261464986
AB  - Humphry Osmond coined the term ‘psychedelic’ in 1956, conjoining ‘psyche’ for ‘soul’ and ‘delic’ for ‘to manifest’ or ‘illuminate’. Soul-illumination is a compound noun that describes a psychological state or process. Osmond intended for it to be a taxonomic noun—naming, not just a state—but a category of drug that can induce this psychological effect as its principal action. Consistent with the etymology of psychedelic, the present work respects the fundamental importance of phenomenology. Accordingly, we examine the main subjective effect of three different psychoactive drugs, psilocybin, ketamine, and MDMA (3,4-methylenedioxymethamphetamine) (variable label, Drug). Over 200 participants rated Delphi-generated subjective rating scale items based on their personal experiences with all 3 drugs. Factor analyses revealed three or four sufficiently independent dimensions of subjective experience (variable label, Effects). A machine-learning classifier successfully predicted Drug from Effects, validating the hypothesis that psilocybin, ketamine and MDMA have categorically distinct subjective effect profiles, differentiable by (1) visions and psychological insight (psilocybin), (2) dissociation (ketamine) and (3) pro-social and loving feelings (MDMA). We conclude that psilocybin is an exemplar psychedelic—a category of drug definable by the induction of a psychedelic state. The quintessential psychedelic phenomenon is a subjective state characterized by visions and psychological insight.
SN  - 0269-8811
SN  - 1461-7285
ER  -