Defining ‘psychedelic’
OpenAlex – December 04, 2025
Source: OpenAlex
Summary
Psilocybin uniquely delivers 'soul-illumination,' characterized by visions and psychological insight, confirming its place as the quintessential psychedelic drug. Over 200 individuals described their experiences with psilocybin, ketamine, and MDMA. Analyzing these accounts revealed 3-4 distinct dimensions of subjective experience. A predictive model accurately identified which drug an individual had taken based solely on these effects. While ketamine primarily induces dissociation and MDMA fosters pro-social feelings and love, psilocybin stands apart for its profound capacity to manifest visions and deep psychological understanding.
Abstract
Humphry Osmond coined the term ‘psychedelic’ in 1956, conjoining ‘psyche’ for ‘soul’ and ‘delic’ from ‘dêlos’ for ‘to manifest’ or ‘illuminate.’ Soul-illumination is an adjective that describes a psychological state or process. However, Osmond’s intention was to use the adjective to name— not just a state— but a category of drug that can induce the subjective effect as its principal action; thus, when used in this way, psychedelic becomes a ‘nominalized adjective;’ describing a ‘thing’ (i.e., a drug) that can induce the described state. Consistent with the etymology of psychedelic, the present work is guided by phenomenology, recognizing its fundamental ontology. Accordingly, we examine the main subjective effect of three different psychoactive drugs, psilocybin, ketamine, and MDMA (variable label, Drug). Over two-hundred participants rated Delphi-derived subjective rating scale items based on their personal experiences with all three drugs. Factor analyses revealed 3 or 4 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 are categorically distinct as determined by their differential ability to induce the following Effects: 1) visions and psychological insight (psilocybin), 2) dissociation (ketamine) and 3) pro-social feelings, epitomized by feelings of love (MDMA). We conclude that psilocybin is an exemplar psychedelic drug— a category of drug definable by the induction of a psychedelic state— the quintessential psychedelic phenomenon. This state is characterized by visions and psychological insight.