The word psychedelic is tricksy. It’s elusive and hard to pin down; tending towards the qualitative rather than quantitative, but over nearly seventy years it has traversed both the aesthetic and the technical. Nearly always, however, by implicit reference to a drug.
A new paper, ‘Proposed Consensus Statement on Defining Psychedelic Drugs’, written by a number of prominent scientists in the field, proposes that only drugs whose actions act upon the 5-HT2A receptor should be considered as psychedelic by the journal in question. LSD, mescaline, psilocybin, the so called ‘classic’ psychedelics, all make the cut. So too, by virtue of some informing, does MDMA and ketamine.
While the journal is of course free to use any definition it so chooses, the choice is not uncontroversial. Psychedelic is tricksy; it eschews simple definition. Notably, in response to the article, Andrew Gallimore has written:


While trying to define a class of drugs through their action on the brain is a neat way to formalize and categorize research, it really misses the essence of the term that they wish to co-opt. As Gallimore noted, anyone familiar with a strong pipe of Salvia divinorum would find this proposed definition inadequate (salvinorin A is a k-opioid agonist). This is the tricksy nature of psychedelic, and the very reason why it has been a useful medical and cultural term; it’s experiential.
Let’s expand an (occasionally wrongly) oft-told story to understand this.
Over the course of March 1956, the British psychiatrist and mescaline researcher Humphry Osmond was writing a paper for a meeting of the New York Academy of Science. Its subject was to be ‘psychotomimetics’—a term meaning ‘to mimic psychosis’ which was then popular in scientific circles to describe the experience of chemicals like mescaline. Osmond believed it to be totally inadequate, ‘absurd’ even, and wished to coin a neologism.[i]
‘The name should have a clear meaning’ he wrote in a letter while composing the paper, ‘be reasonably easy to spell and pronounce and not be too like some other name.’ He mulled over several quite extraordinary words that nevertheless didn’t quite fit the bill: psychophrenics, psychorhexics, psychohormics, euleutheropsychics. He did rather like psychodelics though, meaning ‘mind-manifestors’, and proposed finishing his paper with,
‘The psychodelics which we possess will one day seem as crude as our ways of using them yet even they can help us to extend our experience far beyond our present ability’.
A tricksy word that had yet to find its final spelling was already vying for its meaning, in this case as an amplifier of human experience. In other words, it was never intended to be a pharmacologically strict category. However, still not totally convinced, on the 24th March Osmond wrote to his fellow expatriate and recent mescaline subject, the author Aldous Huxley, asking if perhaps he had any useful suggestions for a term.
The author replied on the 30th March, but had apparently misread Osmond’s suggestion as ‘psychodetic’, which would mean ‘mind-dividing’ (perhaps a good descriptor for when your dose just isn’t quite enough?). Instead, Huxley suggested the word phanerothyme—roughly to ‘make the soul manifest’—in a rhyming couplet: ‘To make this trivial world sublime / Take half a gramme of phanerothyme.’ A term aimed at the aesthetics of the drug experience.
This of course led to Osmond’s famous reply in early April, which capitalized his suggestion by way of correction—of both Huxley’s reading and apparently his original spelling: ‘To fathom Hell or soar angelic / Just take a pinch of PSYCHEDELIC’. It’s not explicit, but perhaps psychodelics was too reminiscent of psychopathy, thus by changing the spelling he would avoid any negative or pre-existing association with other words.
(It’s all Greek to me, of course—although my eminent editor Nikki Wyrd has kindly informed me that the difference lies between ‘of the mind’ and simply ‘mind’.)
However, despite the clear declaration, the question was not immediately settled. Several months later in June, Osmond still employed both terms in his letters to Huxley (12 June, 1956), but by the end of July, each writer had settled on using the descriptor psychedelic in their letters to one another. What is crucial here is that psychedelic is more akin to psychotomimetic than, say, a classification based on either chemical structure or brain interaction: it’s experientially descriptive.
Driving this point home, when Osmond finally published his aforementioned article,[ii] which aside from being an excellent rundown of research, also put pay to the exclusivity of the psychotomimetic reading. In it, he admits that they knew only vaguely about the correlations between physical and mental changes. True, we know much more today thanks to technological advancement, but even then this wouldn’t have been enough for Osmond.
The 1950s was a curious moment in history, he believed, that favoured a psychiatric and pathological bias. While useful for the human sciences, like psychology and sociology, psychedelic also spoke to aesthetics, philosophy and religion, stressing that various accounts demonstrate the ‘unique quality’ of the experience. While he had first wanted a term with a clear meaning, he ended up proposing one that was so inclusive as to verge on ambiguous.
It is this ambiguity that the journal wishes to expunge by its proposed definition of psychedelic drugs. The authors, to their credit, are certainly aware of the extra-pharmacological questions. Grof’s ‘non-specific amplifiers’ gets a nod, as does the mystical experience. But still, what about that strong pipe of Salvia divinorum? It’s not very mystical, it’s more transporting than amplifying, yet it’s definitely, albeit curiously, psychedelic.
You can’t easily bottle experience: it is individualized, cultural, in short, contextual. Indeed, perhaps the most endearing quality of psychedelic is that what it refers to is not easily categorized, but is multitudinous and protean. Psychedelic is a tricksy word for a tricksy experience, and certain drugs embody this trickiness uniquely. Chemical structure and action might indicate a psychedelic experience, but in the end you’ll have to try the drug to be sure.
[i] See Bisbee et al. (2018) Psychedelic Prophets: The Letters of Aldous Huxley and Humphry Osmond. Montreal: McGill-Queen’s University Press. 260-275 for the following quotes.
[ii] Osmond H (1957) ‘A review of the clinical effects of psychotomimetic agents’ in Ann N Y Acad Sci. 1957 Mar 14;66(3):418-34