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Can psychedelic experiences help us understand and explore the mystery of the near-death experience (NDE)? Cultures around the world have associated the two: the South American DMT-based brew ayahuasca is “vine of the dead” in the Quechua language, with the Tukano and Shipibo people believing it allows a transition towards a state of direct communication with the spirits of the deceased; some North American indigeous societies consume peyote (a cactus containing the psychedelic mescaline) to allow them a glimpse into their conception of an afterlife; and the Bwiti people of Gabon employ the bark of Iboga (which contains the potent hallucinogenic tryptamine ibogaine) to induce “near-death“ trances. (For more details on the use of psychedelics by ancient cultures, see Paul Devereux’s The Long Trip: A Prehistory of Psychedelia).

Even in modern society there has been discussion of the similarities between a variety of psychedelic ‘trips’ and the afterlife ‘journey’ of near-death experiencers: from LSD, to ketamine, to DMT (that crossover is evident in the iconic cover artwork of Rick Strassman’s, DMT: The Spirit Molecule – sampled at the top of this post – which features the fantastic painting by Alex Grey titled Dying).

However, this association between psychedelic experiences and NDEs is generally based only on anecdotal evidence and subjective opinion based on a few perceived links. But a new study – “Neurochemical models of near-death experiences: A large-scale study based on the semantic similarity of written reports” – has set out to quantify the possible links by comparing a bunch of NDE accounts (625) with a huge number of ‘trip reports’ (more than 15,000) “spanning experiences with 165 psychoactive substances of ten different pharmacological classes”.

Contributing authors on the study include experts in both fields who readers of this site would be familiar with – including NDE researcher Bruce Greyson, and Earth and Fire Erowid whose Erowid website was used as the source for the trip reports. Natural language processing (NLP) tools were used to evaluate the similarities between the experiences and rank them.

The research project found that the most common substance category in the top 20 with similarities to the near-death experience was that of the serotonergic psychedelics (ayahuasca, peyote, mescaline, etc). However, individually…

…the dissociative psychedelic ketamine presented the highest similarity to NDE reports, followed by [Salvia] divinorum, and a series of naturally occurring (L. williamsii, 5-MeO-DMT, Psilocybe spp., DMT, iboga, ibogaine, ayahuasca, mescaline and E. peruviana), semi-synthetic (LSD) and synthetic (5-AcO-DMT, DPT) serotonergic psychedelics. Other dissociatives that ranked among the top 20 substances were nitrous oxide, PCP and methoxetamine. The only deliriants were the plants of the Datura genus.

Conversely, the 20 substances with the lowest similarity to NDE narratives only included one serotonergic psychedelic (2C-T-21), and neither deliriants nor dissociative psychedelic. Most of the substances were either sedatives or stimulants.

Chart of similarities between various psychedelic trips and NDEs

A calculation of the average ranking for each substance type found that dissociatives ranked first, followed by deliriants and serotonergic psychedelics, and that “all hallucinogens (e.g. dissociatives, deliriants and serotonergic psychedelics) presented a significantly higher average ranking than sedatives, stimulants and antipsychotics/antidepressants.”

So what does all this mean? Firstly, I think it really needs to be remembered that this study is simply looking at semantic similarities – so there’s a whole lot of ‘comparison’ that’s not being done. But in terms of identifying the substances that are most similar, the researchers note various theories that suggest they (or similar compounds) might be released naturally by the brain at the time of death.

For example Rick Strassman hypothesized that NDEs might be caused by the release of DMT from the pineal gland at the time of death, though there has so far been little supporting evidence for this. Other studies have established that ketamine shows neuroprotective and neuroregenerative effects in humans, which has led researchers including Karl Jansen “to suggest that an endogenous ketamine-like compound is released at times of stress and is responsible for the remarkable similarities between ketamine-induced experiences and NDEs.”

As to the ‘big question’ that most of the public would like answered, this study provides no answers as to whether the near-death experience is truly a look beyond, or simply an artifact of a misfiring, dying brain. And the authors are clear about that. They note that although their discussion of psychedelic effects is naturally “biased towards the discussion of neurochemical models of NDEs”, that it should not be read as evidence for a purely neurochemical basis to near-death experiences. “Neurochemical models of NDEs can be theoretically attractive,” they warn, “however, we must emphasize that the analyses conducted in the present work neither validate nor refute these models.”

Nevertheless, the paper then discusses the question of why such neurochemical effects – whether via psychedelics, or an endogeous chemical released when the body is dying – occur…and how they might be used to our advantage (ie. in using psychedelics with the terminally ill):

Regardless of the validity of different neurochemical models of NDEs, a very interesting question was posed by R. Strassman: “if so, so what?“. In other words: even if the validity of one of these models is confirmed, why is neuroprotection linked to substances such as ketamine-like compounds and/or DMT, which are also known to elicit an altered state of consciousness frequently characterized by feelings of bliss and transcendence? Why is neuroprotection by endogenous substances not associated with unconsciousness, or with feelings of distress and aversion?

It has been shown that decreased fear of death can be a long-term consequence of NDEs; thus, NDEs seemingly lack adaptive value. However, this conclusion relies on the assumption that decreased fear of death leads to less caution or increased risktaking behavior. Also, it could be argued that elderly individuals are more likely to experience health problems leading to NDEs, and that feelings of aversion towards death could result in the prolonged competition for resources with individuals who have more potential to reproduce. Furthermore, NDE-dissociative episodes might mitigate PTSD symptoms linked to other dissociative experiences and NDE experiencers seem to endorse more anti-suicidal attitudes as compared to non-NDE experiencers who have come close to death, thus adding support to the potential adaptive value of these experiences.

In any case, drugs that mimic NDE phenomenology might also reduce death-related anxiety, suggesting a potential therapeutic use for the terminally ill. Evidence exists that certain drugs whose reported subjective effects present a high semantic similarity to NDE reports can alleviate end-of-life anxiety in patients with advanced stage cancer, i.e. psilocybin, LSD and ketamine.

In conclusion, the researchers note, their semantic comparison between NDE narratives and psychedelic trip reports provides evidence “that ketamine (and to a lesser extent different serotonergic psychedelics and deliriant alkaloids) can produce an altered state of consciousness resembling near-death.” They warn, however, that it is still “neither possible to corroborate nor refute the hypothesis that the release of an endogenous ketamine-like neuroprotective agent underlies NDE phenomenology.”

Overall, however, they say that the results do provide evidence that ketamine and other psychoactive substances, “result in a state phenomenologically similar to that of ‘dying’ (understood as the content of NDE narratives)”, and that this could have “important implications for the pharmacological induction of NDE-like states fo scientific purposes, as well as for therapeutic uses in the terminally ill as means to alleviate death anxiety.”