I want to think about three sacred plants — the ayahuasca drink, the peyote cactus, and the teonanácatl mushroom. These plants — well, actually, one of them is a fungus — are often discussed in terms of their single active molecule — dimethyltryptamine, mescaline, and psilocybin respectively.

Sacred plants such as these are commonly categorized by the chemical structure of their single active molecule. Thus peyote is categorized by the phenethylamine core of its mescaline molecule; ayahuasca and teonanácatl are categorized by the tryptamine cores of their dimethyltryptamine and psilocybin molecules. This classification also relates the plants to their putative physiological effects. The action of peyote is categorized as catecholaminergic, because the phenethylamine core of mescaline resembles the catecholamine neurotransmitters dopamine and norepinephrine; the action of ayahuasca and teonanácatl is classified as serotonergic, because their tryptamine core is the same as that of the neurotransmitter serotonin.

But the relationship between structure and effect is far from clear. A very rapid tolerance, known as tachyphylaxis, is produced on repeated administration of mescaline and psilocin, the psychoactive metabolite of psilocybin; yet no such tolerance develops for the hallucinogenic effects of DMT. So, despite their similar tryptamine cores, there are significant physiological differences between psilocybin and dimethyltryptamine. At the same time, cross-tolerance occurs between mescaline and psilocybin, but not between either of these and DMT. So, despite their differing tryptamine and phenethylamine cores, there are significant physiological similarities between psilocybin and mescaline.

Moreover, most academic research on these plants ultimately derives from experimentation with lysergic acid diethylamide-25. LSD was, after all, clearly a single active molecule, very potent, and more or less readily available. But LSD is also atypical in many ways. Although usually classified as a tryptamine, it is structurally anomalous, containing both phenethylamine and tryptamine structures. Moreover, as opposed to both phenethylamine and tryptamine hallucinogens, in which the C—N—N chain is conformationally flexible, the C—C—N chain of LSD is incorporated into a more complex and rigid ring structure. Because of this hybrid structure, LSD, unlike the other tryptamines, binds not only to serotonin receptors but to dopamine and epinephrine receptors as well. Some researchers therefore have proposed a special class of ergolines, as opposed to simple tryptamines, which would include LSD and a few very closely related compounds.

Despite all this, there has been a pervasive assumption among academic researchers that the psychedelic experience is paradigmatically that of LSD, and that the experience of dimethyltryptamine, mescaline, and psilocybin can be lumped together with that of LSD under such rubrics as altered state of consciousness. Such terms refer vaguely to what the experiences of taking LSD, mescaline, dimethyltryptamine, and psilocybin — and maybe DOM and MDMA, but maybe not — presumably have in common. That there is such a common experience is simply assumed. Of current researchers, apparently only Richard Glennon has attempted a typology, based primarily on animal drug discrimination studies, which classifies these substances as hallucinogenic, central stimulant, or other, with some substances occupying more than one category.

I think we need a better typology than that. The goal should be to understand the phenomenology of the sacred plants under their ceremonial conditions of use, not when their single active molecules are ingested under experimental or recreational conditions. These three sacred plants seem like a good place to start thinking about such an experiential typology.

I think it is pretty clear that the effects of the ayahuasca drink, the peyote cactus, and the teonanácatl mushroom are phenomenologically distinct. I think that one way to capture those differences is to think of their effects — indeed, the effects of all sacred plants — as lying within a three-dimensional space defined by three distinct axes, which I will call here hallucinogenic, empathogenic, and entheogenic. Within this three-dimensional space, of course, there can be gradations and combinations; it is as if each sacred plant had three slider bars, labeled hallucinations, empathy, and insight, which could be adjusted independently.

It seems to me that ayahuasca is paradigmatically high on the hallucinogen axis, peyote on the empathogen axis, and teonanácatl on the entheogen axis. While all three sacred plants share certain effects, predominantly visual distortions and often brightly colored geometric illusions, the experience of each lies at a unique point in this three-dimensional experiential space.

The ayahuasca drink produces visual experiences of objects and people that are solid, detailed, three-dimensional, animated, interactive, and embedded in ordinary perceptual space; and auditory experiences which are immediate, external, directional, locatable in space, and often coordinated with visual experiences. Ayahuasca, then, can reasonably be said to paradigmatically hallucinogenic. Although LSD, mescaline, and psilocybin — what we can call the classical psychedelics — have also been called hallucinogens, there is a general consensus that this term is inappropriate.

Thus, in many studies of these classical psychotropics, hallucinations — that is, perceptions “to which the subjects reacted as real” — were rarely reported and were considered a minor consequence; the vivid, mostly geometric visual illusions that are one of the hallmarks of the classical psychedelics “are seldom perceived as having real outside existence.” Researchers Peyton Jacob and Alexander Shulgin went so far as to say that, for these classical psychedelics, the term hallucinogen is today “allowed as a euphemism, although that term is also inaccurate because hallucinations are not part of the usual syndrome.” Another researcher, David Nichols, agreed: “Hallucinogen is now, however, the most common designation in the scientific literature, although it is an inaccurate descriptor of the actual effects of these drugs.”

Jonathan Ott, R. Gordon Wasson, and others famously proposed the term entheogen for these classical psychedelics, instead of the term hallucinogen, because, as Ott explicitly stated, the “shamanic inebriants did not provoke hallucinations.” Rather, said Ott, the classical psychedelics produced “transcendent and beatific states of communion with deity.” The term entheogen, meaning something like realizing the divine within, was intended to refer to the primarily cognitive depth- or insight-producing nature of the LSD experience.

These entheogenic experiences are frequently characterized by the psychoanalytic term oceanic feeling — as a dissolution of ego boundaries, a peak experience, a mystical experience, oceanic boundlessness, a temporal and spatial expansion of consciousness beyond the usual ego boundaries. Such experiences often give a sense of having attained a deeper understanding or new revelation concerning some important topic, such as the nature of existence or the qualities of God. Daniel Freedman, in an influential paper published in 1968, speaks of the experience in terms of portentousness — “the capacity of the mind to see more than it can tell, to experience more than it can explicate, to believe in and be impressed with more than it can rationally justify, to experience boundlessness and ‘boundaryless’ events, from the banal to the profound.” Just as ayahuasca is paradigmatically hallucinogenic, the teonanácatl mushroom is paradigmatically entheogenic in just this sense.

Descriptions of such entheogenic experiences are clearly different from those given for ayahuasca. It may be worth adding that the famed Amazonian ethnobotanist Richard Evans Schultes drank ayahuasca scores of times, but claims never to have had a “mystical experience.” Rather than any earth-shaking experience, he once told William S. Burroughs, “all I saw was colors.” Even making allowances for Schultes’s rather dry Harvard wit, the distinction is clear.

In the same way, in 1983, Ralph Metzner coined the term empathogen — as opposed to both hallucinogen and entheogen — to denote the designer drug MDMA and some of its phenethylamine relatives, whose effect is primarily to induce feelings of empathy. In 1986, David Nichols proposed the alternative term entactogen, meaning something like producing a touching within. His motives were primarily tactical: he believed that empathogen sounded too much like pathogen. He also thought the earlier term was too limiting, since clinical use of MDMA was intended to go beyond the enhancement of empathy.

Interestingly, the phenethylamine core of mescaline is most closely shared, not with the other classical psychedelics, but rather with MDMA, the exemplary empathogen. Indeed, some users maintain that, as a class, the phenethylamines are more sensual, emotional, and interpersonal than the more cognitive, abstract, and ideational tryptamines. Such empathogens create feelings of warmth, sympathy, and closeness with other people. While the experience of the peyote cactus includes entheogenic components, a significant part of the experience, especially in a social setting, as in a ceremony of the Native American Church, is emotional and relational rather than cognitive — paradigmatically empathogenic.