Philosophy of Psychedelic Therapy: Existential Medicine or Comforting Delusion?

Written by Chris Letheby, Ph.D.

In the ever-accelerating psychedelic renaissance, one question has attracted the bulk of the attention: Do psychedelics (plus psychotherapy) safely and effectively reduce psychiatric symptoms? Another question has seen far less attention, but is equally interesting: Are the things that people experience on psychedelics real? Do these substances induce genuine insights into self and world, or just hallucinations and delusions? Are the spirit world or the cosmic consciousness really out there, existing, independent of our beliefs – just like Joe Biden and the planet Neptune? Or are they figments of our imagination, like the characters of dreams and literary fictions? Is psychedelic therapy, in Charles Grob’s (2007) phrase, an “existential medicine?” Or is it, as Michael Pollan (2015) wondered, “simply foisting a comforting delusion on the sick and dying?” (Here I focus solely on “classic,” serotonergic psychedelics, such as LSD and psilocybin.)

This question was debated in the first, mid-20th century wave of psychedelic psychiatry. In 1963, Willis Harman ascribed the perceived unacceptability of psychedelic therapy to a “fundamental empirical fact: Through the psychedelic experience persons tend to accept beliefs which are at variance with the usual conception of the ‘scientific world view.’” (Harman, 1963). In 1974, the philosopher Robert Nozick introduced his famous thought experiment about the Experience Machine, a virtual-reality system that can give you the richest, most satisfying simulated life imaginable. Nozick (1974) argued that it would be a mistake to plug in, because pleasure and pain are not the only things that matter for a good life: it also matters that our beliefs are founded in reality. The thought experiment aims to undermine the hedonist view that only pleasure and pain matter for well-being. Interestingly, Nozick relates the Experience Machine to the ongoing debate over “psychoactive drugs,” by which I believe he means psychedelics. He explains the “intensity” of this debate as follows: some people view psychedelics as akin to the Experience Machine – a route to a satisfying but fake reality – while others see them as a path to a deeper, more authentic reality.

Why have these questions gained comparatively little attention in the recent wave of research? It is tempting to speculate about changing cultural currents, about a postmodern scepticism regarding truth and knowledge, and about the “post-truth” era of alternative facts and online conspiracy theories. Some have argued that the epistemic status of psychedelic experiences is relatively unimportant compared to their therapeutic benefits (Flanagan and Graham, 2017). This may be so, but it does not show that truth and knowledge are completely unimportant and can simply be ignored. Indeed, this is one of the points of Nozick’s Experience Machine.

Another point that sometimes gets raised is that we can never know for certain whether psychedelic insights are accurate or not – but certainty is a red herring. The jurors in a criminal trial can never know for certain whether the defendant is guilty, but we all understand that it is possible and important to try to determine the most probable hypothesis using evidence and reason. The same point applies to virtually every decision we make in our lives. One of the great lessons of the last few centuries of epistemology, the philosophical study of knowledge, is that complete elimination of doubt is unattainable, but unnecessary: infallibility is not a prerequisite for reliable knowledge. Making decisions and forming beliefs under uncertainty is just the human condition. We cannot know for sure which answer is true, but this need not and should not stop us making a serious, rational attempt to figure out, tentatively, which answer is probably true. 

In my book, Philosophy of Psychedelics (Letheby, 2021), I approach this project from the perspective of philosophical naturalism. The term “naturalism” has different meanings in different academic disciplines, but in contemporary English-language philosophy, it often denotes the view that the natural world studied by science is all that exists. How exactly to define “natural” is a difficult question. But most versions of this view endorse a materialist or physicalist account of mind, holding that consciousness is an outcome of complex development, rather than being basic or fundamental in the universe. So, according to naturalism, there is no cosmic consciousness, no spirit world, and no literally existing “discarnate entities” (Luke, 2011).

Of course, one of the most common apparent insights induced by psychedelics is that there is some deeper level of reality than the everyday empirical world. The longstanding traditions of ritual psychedelic use in non-Western cultures typically embed this use in metaphysical frameworks that posit the literal existence of spirits and the spirit world (Winkelman, 2021). Echoing this view, the religious scholar Huston Smith said: “The central message of the entheogens [is] that there is another Reality that puts this one in the shade” (2000, p. 133). Since my project is to pursue a naturalistic understanding of psychedelic therapy, I do not engage in detail with these traditions and frameworks. But why pursue a naturalistic account? Why not take this apparent insight at face value and reject naturalism?

 A full answer to this question would require delving deeply into issues in metaphysics, epistemology, and related areas. But there are two basic reasons. First, naturalism is a simpler, more parsimonious views than alternatives which posit another reality. Second, there is no compelling evidence that disembodied entities or cosmic minds exist. Of course, we still lack a convincing naturalistic explanation of conscious experience itself— the so-called Hard Problem (Chalmers, 1995). But this does not prove much, in itself. The scientific study of consciousness is relatively young, and all fields have unsolved problems. Still, one might wonder, why not take psychedelic experiences themselves as strong evidence against naturalism? My basic answer is that a naturalistic worldview has the resources to explain the many strange and striking features of psychedelic experience that often prompt non-naturalistic interpretations. This is something I try to show in the book.

Where does this leave us with respect to our initial question? Is psychedelic therapy, after all, simply foisting a comforting delusion on the sick and dying? Not so fast. Suppose, for argument’s sake, that my brand of naturalism is true. Given that assumption, if psychedelic therapy were to alleviate psychiatric symptoms mainly by inducing comforting beliefs in “another Reality”, then it would work mainly by the induction of false beliefs. But, I argue, this is an implausible account of how psychedelic therapy works. It seems plausible initially, given the well-established correlation between ratings of mystical-type experience and good clinical outcomes. But the picture becomes more complicated when we examine the kinds of experiences that are being captured by the relevant psychometric questionnaires. Many psychedelic therapy patients do not emphasise metaphysical epiphanies or encounters with another Reality (Breeksema et al. 2020). Some patients report experiences of this kind, but others do not. More consistently emphasised are emotional breakthroughs, psychological insights, feelings of connectedness and acceptance, and changes to the sense of self. In short, the relevant psychometric instruments cast a broad net.

So, I argue that psychedelic therapy does not work mainly by changing people’s metaphysical beliefs—even though it sometimes does that. Rather, it works mainly by disintegrating mental representations of the self, which can become rigid and dysfunctional in mental disorders; this allows these self-representations to be revised for the better (Letheby and Gerrans, 2017). By stepping outside her ordinary self-conception and seeing its constructed nature, the psychedelic therapy patient can access alternative self-conceptions: the person with substance use disorder can imagine a less chaotic future for herself; the depressed or anxious person can experience a return of hope and vitality, or a world that does not present as fundamentally threatening and unsafe.

Interestingly, this process of revising the “self-model” involves the acquisition of genuine forms of knowledge  that are compatible with naturalism. Often, when we think about knowledge, we think of “factual” or “propositional” knowledge – knowing that certain things are the case. A textbook example is knowing that Paris is the capital of France. It is possible that many psychedelic therapy patients acquire propositional knowledge about their own minds, such as psychodynamic insights into their previously unconscious emotions and motivations – though even insights of this kind can turn out to be false. (Sober scrutiny, assisted by a therapist, provides a valuable check.) But there are other kinds of knowledge, too. Notably, there is “ability” knowledge, or knowledge how – what we have when we know how to ride a bicycle, or how to speak Arabic. There is evidence that psychedelic therapy patients acquire certain kinds of ability knowledge through their experiences – notably, knowledge how to relate to their own thoughts and feelings in open, accepting ways, similar to the attentional skills cultivated in mindfulness meditation.

A third type of knowledge discussed by philosophers is knowledge by acquaintance, which roughly  involves knowing something directly, or experientially, rather than via book-learning or others’ testimony. There are important facts that are easy to know about indirectly, by reading the reports of mystics and psychonauts, but harder to know about directly – such as the human mind ’s potential for profound wonder and ecstasy, and the constructed nature of the ordinary sense of self. Many psychedelic therapy patients go from having only indirect knowledge about their minds’ potential to being directly acquainted with this potential as it becomes manifest in their field of consciousness. Finally, in a similar vein, psychedelic experiences can help patients acquire new knowledge of old facts. Certain facts that they already knew in an intellectual manner, such as the inevitability of death or our interconnectedness with the natural world, can be known in a new way. As one patient put it, the psychedelic experience “brought [her] beliefs to life, made them real, something tangible and true” (Malone et al. 2018, p.4).

One of the main conclusions of my book is this: From a naturalistic perspective, psychedelics can be both existential medicines and agents of comforting delusions. However, when it comes to their current therapeutic use, the former term is more apt and accurate. Psychedelics do not reduce psychiatric symptoms mainly by changing patients’ metaphysical beliefs, but by facilitating a transformative re-appraisal of fundamental assumptions about the self, the world, and the relations between the two. Moreover, this process involves genuine knowledge acquisition – so even from a naturalistic perspective, psychedelic therapy confers substantial epistemic benefits, as the philosophical jargon has it.

Dr. Chris Letheby is a philosopher working on issues related to the therapeutic and transformative potential of classic psychedelic drugs.  In his work, Letheby argues that a traditional conception of psychedelics as agents of insight and spirituality can be reconciled with naturalism, the philosophical position that the natural world is all there is. He is currently Lecturer in Philosophy at the University of Western Australia and Postdoctoral Researcher at the University of Adelaide on the Australian government-funded project “Philosophical Perspectives on Psychedelic Psychiatry.” His monograph, Philosophy of Psychedelics, was published in 2021 by Oxford University Press.


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