Defining 'psychedelic'.

Abstract

Humphry Osmond coined the term 'psychedelic' in 1956, conjoining 'psyche' for 'soul' and 'delic' for 'to manifest' or 'illuminate'. <i>Soul-illumination</i> 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 <i>psychedelic</i>, the present work respects the fundamental importance of phenomenology. Accordingly, we examine the main subjective effect of three different psychoactive drugs, <i>psilocybin</i>, <i>ketamine</i>, and <i>MDMA (3,4-methylenedioxymethamphetamine)</i> (variable label, <i>Drug</i>). 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, <i>Effects</i>). A machine-learning classifier successfully predicted <i>Drug</i> from <i>Effects</i>, validating the hypothesis that <i>psilocybin</i>, <i>ketamine</i> and <i>MDMA</i> have categorically distinct subjective effect profiles, differentiable by (1) <i>visions</i> and <i>psychological insight</i> (<i>psilocybin</i>), (2) <i>dissociation</i> (<i>ketamine</i>) and (3) <i>pro-social</i> and <i>loving feelings</i> (<i>MDMA</i>). We conclude that <i>psilocybin</i> is an exemplar <i>psychedelic</i>-a category of drug definable by the induction of a <i>psychedelic state</i>. The quintessential psychedelic phenomenon is a subjective state characterized by <i>visions</i> and <i>psychological insight</i>.

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