The term 'psychedelic' was coined in 1956 from Greek roots meaning 'soul-manifesting' or 'soul-illuminating,' intended to name a drug category defined by its ability to induce a characteristic subjective state. This study examined the main subjective effects of psilocybin, ketamine, and MDMA. Over two hundred participants rated items about their experiences with all three drugs. Factor analyses revealed three or four independent dimensions of subjective experience. A machine learning classifier successfully predicted which drug a person had taken from the effects reported, confirming that the three drugs produce categorically distinct experiences: psilocybin induces visions and psychological insight, ketamine induces dissociation, and MDMA induces pro-social feelings such as love. Psilocybin is thus an exemplar psychedelic drug, definable by its induction of a psychedelic state characterized by visions and insight.
A cognitive-linguistic analysis of interviews with a healthy volunteer after moderate-to-high psilocybin doses reveals that the participant consistently used metaphors framing abstract introspective events in terms of concrete, visible, and interpersonal events, instantiating a cognitive frame called the Observer's Model. These metaphors imply cognitive defusion and heightened metacognitive awareness during the sessions. Literal descriptions of hallucinatory visual experiences correlated semantically with metaphorical expressions, suggesting metaphorical thinking plays a role in motivating those experiences. The findings are linked to neuroscientific research on psychedelics and have psychological and therapeutic implications.