This Is Your Brain on Drugs:

What is, or what should be, a philosophy of psychedelics? This question has never been so broadly relevant, given the groundswell of mainstream interest and experimentation, scientific investigation, therapeutic trials, entrepreneurial enterprise, and decriminalization of natural psychedelics in several American states. Chris Letheby’s Philosophy of Psychedelics is the first monograph to apply the term as an unelaborated title that, with the backing of Oxford University Press, projects the authority of a wide-ranging academic urtext that could define a renewed and newly legitimate field of inquiry.

The title proves to be something of a misnomer, however, as Letheby deliberately avoids philosophizing on the nature of mind, subjectivity, or psychedelic experience, as well as referencing philosophers who do; as a “card-carrying naturalist,” there is literally nothing of real metaphysical value for him to speculate upon. So, the discussion is narrow and notable for the breadth it excludes. A Naturalist Philosophy of Psychedelics may have been more representative of its limited purview, which nevertheless serves as a useful survey of psychological research on psychedelic therapies up to the time of writing. And yet in recognizing this, it does seem miscategorized as a primarily philosophical work; indeed, absent Letheby’s explicit articulation of his hard naturalist stance, often taken as a given in the scientific community and so left unstated, the work would be better categorized under psychology.

One trend among some naturalist philosophers of mind is that working theories of consciousness, knowledge, and existence must fundamentally agree with and extend from modern science alone. Letheby subscribes to an especially strict definition, arguing that “the naturalising programme in philosophy attempts to show that various phenomena central to human life . . . are unmysterious parts of the natural world investigated and described by the sciences” (197). And yet this is not exclusively representative: There are less conservative approaches that at least do not outright deny the possibilities of such metaphysical implications, such as Ganeri’s liberal naturalism and McDowell’s critique of “bald” or “rampant” naturalism, of which Letheby’s would be an example.^[1] This century has seen many humanistic disciplines—Philosophy and Religious Studies included—become fodder for late-night punchlines and social media memes. Assailed as overly intellectual and professionally impractical fields of study, I once saw “Starbuck’s barista” inscribed under a campus bulletin advertising, “What you can do with a philosophy major.” In an environment where the value of the Humanities is increasingly challenged, some philosophers of mind seem to have ceded their own field while attempting to carve out a new niche beyond it. Letheby is not trained as a research scientist in Psychology or Neuroscience, but the book successfully demonstrates his facility with these fields (indeed, the vast majority of his cited sources are from these disciplines) as well as how a critically trained philosopher can contribute to them.

Letheby initiates his argument by introducing his primary thesis that the phenomenological force of psychedelic experience betrays the epistemic innocence of the subject who accepts metaphysical insights as reliable—and all the more so when they are therapeutically effective. The second chapter targets specific types of transcendent experiences, such as self-dissolution, for naturalist reframing, which is then advanced by batteries of neuroscientific data in chapter 3. The next two chapters present key aspects of his argument: Chapter 4 presents his “Epistemology of Psychedelic Experience,” where the noetic quality of subjective certainty does not qualify as objective truth, and chapter 5 acknowledges—and appreciates—the therapeutic potential of psychedelic experience despite its promotion of non-literal beliefs, thus challenging the “comforting delusion objection.” Chapter 6 presents the self as a constructed model that can be disrupted and remodeled by psychedelics, empowering the transformation of treatment-resistant pathologies grounded in identity. In the final three chapters, he advocates a naturalized spirituality replete with awe (in chapter 7) and meaning (in chapter 8) despite the denial of all non-naturalized metaphysical claims, which is further articulated and defended in chapter 9’s conclusion.

The foremost topic that leans toward the more traditionally philosophical concerns psychedelic-induced spiritual experiences, but in ascribing to metaphysical naturalism or naturalized spirituality, Letheby’s “aim is thereby to show that certain familiar or important features of our lives and the world do not require us to believe in anything non-natural or supernatural, but are ultimately unmysterious parts of the one closed causal system described by the natural sciences” (35). Resolutely denying the existence of anything supernatural, metaphysical, mystical, sacred, or divine beyond the purview of secular materialism, he simultaneously dismisses any and all experiences of such phenomena, whether through sober religion or psychedelic doses, as subjective misinterpretations of aberrant neural activity. Part of the challenge is that, while tripping, “the brain may visit states in which it represents its own informational state as highly precise or reliable” when, according to Letheby, it is anything but (108). He does not deny that they experientially occur to subjects, nor that their personal and therapeutic effects can be profound, but rather that the metaphysical referents of those experiences categorically do not exist. In a word, they are hallucinatory.

For naturalists, a significant issue arises when conceding that the uniquely transformative potential of psychedelic therapies—the very efficacy that sets them apart from conventional medicines—is often correlated to the spiritual experiences induced by them. In contemplating the ethics of psychedelic therapy for terminal patients suffering depression, Michael Pollan asked, “is psychedelic therapy foisting a comforting delusion on the sick and dying?” (3).^[2] Terminal patients have achieved durable relief through acceptance of death, instigated by psychedelic experiences that irrefutably confirm, for them, transcendence beyond the mundane, material dichotomies of life and death. Like Letheby, Pollan maintains a “staunchly materialist” stance, so his concern here reflects his skepticism toward the authenticity of psychedelic experiences.^[3] The question, then, is how that in/authenticity is relevant therapeutically, epistemically, and ethically.

Letheby centers the novel value of his discussion on a “relatively unexplored response to the comforting delusion objection,” where he applies Lisa Bortolotti’s concept of epistemic innocence to psychedelic-induced spiritual experiences (3). His position is not only that the therapeutic benefits outweigh the epistemic risks, but that the former are now well-documented while the latter are typically overstated. To make the second claim, he isolates mystical experience from subsequent beliefs about it and argues that one need not follow the other. Employing Metaphysical Alief Theory, where alief “refers to a mental representation of the world that is not reflectively endorsed or believed, but nonetheless influences thought, emotion, and action” (76), Letheby “ascribes lasting benefits to the psychedelic-induced vision of a Joyous Cosmology—that is, to the metaphysical hallucination itself and memories of it, irrespective of whether the subject believes it to be veridical” (62). He therefore advocates post-trip therapeutic processing, apparently with the expectation that many patients would arrive at the same nuanced, naturalist conclusion as himself. But how would alief processing be applied in practice? Many patients (never mind “recreational” psychonauts) report these psychedelic experiences to be among the most important experiences of their entire lives: How is it ethical for a naturalist clinician to foist their discomforting conclusion upon their patients?

The majority of people throughout the duration of human existence up to the present have ascribed to some form of religious ideology (just applying this terminology distances itself from practice and experience, where it is more simply known and applied as “truth”). Even today, while there are growing populations of naturalist “nones,” agnostics, and unaffiliated, highly individuated “SBNRs” (spiritual but not religious), 69% of American adults still identified with a specific religious sect in 2023–24.^[4] Rampant naturalists therefore occupy an extreme historical minority, and yet their own truth claims rely on rhetorical strategies similar to the religious ideologies that continue to compete with them, never mind the fact that rational argumentation and the rigorous interrogation of empirical evidence have been central to spiritual traditions such as Indian and Tibetan religio-philosophical debates for well over a thousand years.

Through the imprimatur of scientific method, secular materialists claim the ideological foundation of modern culture not only now but for the future. It is often presented as the truest, even when fundamental questions concerning the relationship of matter and consciousness remain stubbornly unresolved by physicalist frameworks, and quantum physics demonstrates the incredible limitations of perception-based assumptions concerning the nature of reality. David Chalmers’s hard problem of consciousness still towers over the fields of psychology, neuroscience, and philosophy of mind, and yet Letheby evangelizes his resolute faith in what may be termed a scientific mysticism, his expectation that naturalism will inevitably answer all questions, resolve all problems, and prove itself thoroughly correct, someday (105). Just like the world’s most popular religions, the rhetoric of exclusivism, universalism, and prophecy pervades Letheby’s naturalism. While “prophecy” is certainly not his intention (“established facts,” valid now and in the future, is likely more palatable to the naturalist), the total dismissal of non-naturalist epistemologies collapses the value of his discussion into a single point that, like many sectarian polemics, risks stagnating without the benefit of broader dialog. Letheby concedes that his book will be outdated by the time of publication, but here he references the rapid advancement of the scientific literature on psychedelics (7); not that the myopia of rampant naturalism may serve to undermine its accessibility, durability, and relevance to what remains, inevitably, an ongoing discussion.

It is important to acknowledge that we are all subject to cognitive bias and cultural framing (155), naturalists, philosophers, and scientists included. Adopting a more pluralistic, compassionate, and informed view of other belief systems, as advocated in cultural studies, invites the possibility of genuine dialog by which all participants can be collectively enriched by learning from each other. However, this requires us to transcend the too often casual arrogance that only our view is correct while all others must be wrong. Such is advocated in India’s Jain tradition, where nonviolence (ahimsa) entails not only abstaining from harmful, externalized actions of body and speech, but fundamental attitudes of mind that assume authority and superiority, whether social (both Jainism and Buddhism reject caste) or ideological. In Jainism especially, sectarian dogma is not only problematic morally but epistemically because of the limitations it inevitably invites (more on this below).

Part of my critique here stems from the veridicality of psychedelic experience not only being a philosophical question but one directly relevant to treatment programs and their participants. As the preeminent guidelines for clinicians in the United States, the code of ethics for both the American Psychological Association (Principle E: Respect for People’s Rights and Dignity) and the American Counseling Association (A.1 Client Welfare: A.4.b Personal Values) are explicit in how professionals are expected to negotiate variant ideologies.^[5] The ACA states:

Counselors are aware of—and avoid imposing—their own values, attitudes, beliefs, and behaviors. Counselors respect the diversity of clients, trainees, and research participants and seek training in areas in which they are at risk of imposing their values onto clients, especially when the counselor’s values are inconsistent with the client’s goals or are discriminatory in nature.

Ideological neutrality is the ethical standard for clinicians of any specialization, psychedelics or otherwise. In upholding the foundational injunction to do no harm, clinicians must not press their own ideology, whatever it may be, upon their patients but help them encode their individual experience with meaning such that they may extract the most profound benefit by means of it.

To be fair, Letheby does not address clinical practice; he does not outline a methodology for applying Metaphysical Alief Theory in therapeutic settings but rather promotes a theoretical stance that would refute the comforting delusion objection among card-carrying naturalists like himself, and perhaps more broadly in the scientific and regulatory communities. This significantly limits the target audience of his book, however, and again indicates that the title is far more inclusive than its content.

Among Letheby’s overarching objectives is advocacy for psychedelic therapies, but the naturalist reasoning for Metaphysical Alief Theory is not only impractical but unethical. If that staunchly naturalist bias were even subtly imposed upon patients—and this would include a dialogical stance that denies the veridicality of their mystical-type psychedelic experience—it would contradict established professional standards. Among other reasons, the relationship between clinician and client is structurally asymmetrical, where epistemic authority already lies with the former; thus, the imposition of views in the therapeutic context is considered abusive. The purpose of therapy is to help the client, not indoctrinate them toward an epistemic position. Moreover, the question must be asked: What is the harm in helping patients interpret their experience in the way most therapeutic to them? Does Letheby expect patients to perform his kind of nuanced, theoretical backflip, where they are led to accept that they touched the heavens while tripping, and yet that transcendent referent is merely the hallucinatory projection of their brain on drugs? And if that referent is deemed unreal, would this not risk the attenuation of psychedelic therapy’s clinical outcomes? If so, this would undermine the primary ground of their advocacy, which is their efficacy.

Interestingly, Letheby highlights specific subtypes of transformational experiences, often reported as mystical, that accord with his naturalist worldview and so do not require metaphysical alief. Buddhists might find a degree of scientific vindication when he highlights self-dissolution and connectedness, not as hallucinatory projections but materially grounded realities. For Letheby, assertions that the self does not exist as it appears, and that all things in the universe process interdependently, are true. Moreover, “the central mechanism of psychedelic therapy is the disruption and subsequent revision of mental representations of the self” (81) because “by experiencing radically different forms of self-modeling, we come to see vividly that the previously unquestioned sense of who I am is just a story, and can be told otherwise” (183). While he makes brief references to Buddhism in several places and cites several studies by Miri Albahari that apply a psychological lens to Buddhist experiences of nonself, Letheby does not fully acknowledge the degree to which his definitions of self and self-dissolution precisely correspond to foundational Buddhist tenets. This is the exact type of missed opportunity risked by staunch naturalism: Not only are most arguments that contradict it ignored, but even those that have much to offer—such as 2500 years of rigorous Buddhist interrogation of the nature of self and selflessness—are barely glossed. Taking up a philosophical inquiry of psychedelics might offer us a chance to critically reflect upon those frameworks we accept (as well as those we reject), but Letheby attempts only to fit the experiences and effects of psychedelics into his assumed framework.

In Indo-Tibetan Buddhist systems, the fundamental problem, the root of suffering itself, is the conviction that self truly exists the way it appears, which is as a singular, continuous, independent entity. Letheby writes that “the ordinary sense of self is contingent, constructed, and mutable” (182), which agrees with Buddhist assertions that what we take to be the self is not singular but composed of parts (constructed), not continuous but ever-changing or impermanent (mutable), and dependent on causes and conditions (contingent). For both Letheby and Buddhist philosophy, this is not subtle but obvious under analysis; another feature of psychedelics is that they facilitate “new knowledge of old facts via novel modes of presentation,” so insight into the true nature of self, and the false or illusory nature of our operative modes of self-conception, are neither metaphysical nor newly profound, no matter how profoundly transformative insight into them may be (184–191).

Likewise, nirvāṇa translates literally as “cessation,” like the extinguishment of a candle’s flame, and signifies the end of suffering. Much evidence suggests that the Buddha and/or early Buddhists did not view this as some kind of heavenly existence, background reality, or what Letheby and Pollan refer to as a “Joyous Cosmology.” It is the mere but total absence of suffering, to which these naturalists would seem to find little objection, so long as it deemphasizes the attendant doctrines of karma and rebirth (assertions of which remain varied and controversial). The point here is not to suggest that Buddhism is correct because modern naturalism agrees with some aspects of it, but rather to emphasize pluralism as a fundamental value and thereby uncover the greatest possible enrichment in a diversity of views.

Since Letheby published Philosophy of Psychedelics, more books from major academic presses have emerged on the topic, some of which directly address psychedelic experience and its veridicality and a few of which boldly rely on critical subjectivity to integrate the author’s own psychedelic experience as relevant enhancement for their more objective inquiries, whether anthropological (see G. William Barnard’s Liquid Light) or philosophical (William A. Richards’s Sacred Knowledge).^[6] Another book well worth mentioning here is Thomas Metzinger’s phenomenology, The Elephant and the Blind, that takes the experience of minimal, reflexive, nondual, nonconceptual, and/or pure awareness seriously.

While the ancient Indian parable referenced in Metzinger’s title disavows philosophical disputation altogether (the blind men come to blows!), he applies it as a warning of the epistemic risks of individual perception and the error of applying it globally.^[7] When each of the blind grasps one part of the animal (such as the narrow tail) and thinks that alone defines an elephant in its entirety, they are left with an impoverished and inaccurate sense of the whole. So returning to the initial question: What is, or what should be, a philosophy of psychedelics? And who would be the most qualified to write one? In interviews, Letheby admits to experimenting with psychedelics earlier in life. However, he and his naturalist colleagues are relatively inexperienced, if not naïve—some of them quite deliberately so. They are afraid that taking psychedelics would corrupt their objectivity, their ability to critically research psychedelics, and, consequently, their professional legitimacy.^[8] While Letheby presents an array of relevant psychological research on the topic, there is a fixation upon just one perspective, like the blind insisting their one part to be definitive while simultaneously denying all other possibilities. Philosophers, psychonauts, and philosopher-psychonauts will find much valuable information here, but for all those who attest that psychedelics offer insight beyond the material, many will insist that Letheby misses the whole in the most profound ways.

Notes

1. Jonardon Ganeri, The Self: Naturalism, Consciousness, and the First-Person Stance (Oxford University Press, 2012) and John McDowell, Mind and World (Harvard University Press, 1994). ↑
2. Michael Pollan, “The Trip Treatment,” The New Yorker (February 9, 2015). DOI: https:// www.newyorker. com/ magazine/ 2015/ 02/ 09/ trip- treatment ↑
3. Michael Pollan, How to Change Your Mind: What the New Science of Psychedelics Teaches Us About Consciousness, Dying, Addiction, Depression, and Transcendence (Penguin Press, 2018), 348. ↑
4. Pew Research Center, “Religious Landscape Study,” accessed June 10, 2026, https://www.pewresearch.org/religious-landscape-study/. ↑
5. American Psychological Association, Ethical Principles of Psychologists and Code of Conduct, amended June 1, 2010, and January 1, 2017 (American Psychological Association, 2017), https://www.apa.org/ethics/code; American Counseling Association, ACA Code of Ethics (American Counseling Association, 2014), https://www.counseling.org/docs/default-source/default-document-library/ethics/2014-aca-code-of-ethics.pdf. ↑
6. G. William Barnard, Liquid Light: Ayahuasca Spirituality and the Santo Daime Tradition (Columbia University Press, 2022) and William A. Richards, Sacred Knowledge: Psychedelics and Religious Experiences (Columbia University Press, 2018). ↑
7. For one possible source of the analogy, see Thanissaro Bhikku, trans., “Tittha Sutta: Sectarians (1),” Access to Insight. https://www.accesstoinsight.org/tipitaka/kn/ud/ud.6.04.than.html. For Metzinger’s account, see Thomas Metzing, The Elephant and the Blind (MIT Press, 2025), XXV. ↑
8. Jessica Lawson, “The Philosophy of Psychedelics—An Interview with Chris Letheby,” Khapi: The Ayahuasca Hub. https://kahpi.net/the-philosophy-of-psychedelics-chris-letheby/. ↑