The term “psychedelic,” used for the first time in 1956 by the British psychiatrist Humphry Osmond (1917–2004), refers, according to its etymology, to a substance that, upon ingestion (or contact with the skin), makes the mind, or soul (Greek: psychê) manifest. Several religions, such as the Brazilian Santo Daime, make ceremonial usage of substances that affect perception and consciousness, and regard as “sacred” their ingredients and the experiences they bring about, as well as the “dimensions,” “entities,” and “teachings” that one supposedly attains through them. A religiously connoted term to define those very substances is “entheogen,” another contemporary (1979) coinage with Greek words that means “generating the divine within.” Hostile or skeptical observers may rather be inclined to regard and describe those very experiences as alterations of the mind's “normal” state and to label their systematic consumption as essentially escapist or hedonistic in character.

William A. Richards is a clinical psychologist and a psychotherapist whose academic training also encompasses theology, comparative religion, and the psychology of religion. In Sacred Knowledge: Psychedelics and Religious Experiences he discusses psychedelics while assuming a confessional viewpoint. The author, in fact, does not represent a specific religious movement or doctrine; however, he takes the above‐mentioned “sacredness” seriously and makes an impressively meticulous and convincing effort in two directions. First, he deconstructs the easy, misguided, and misleading equation between psychedelics and “drugs”—a highly questionable term per se since substances that display the same characteristics of ones forbidden by law are often marketed freely, such as alcoholic drinks (most psychedelics, including substances considered sacred, are controlled as illegal psychoactive drugs in most Western countries). Secondly, Richards provides his readers with thought‐provoking suggestions for the cross‐pollination of studies about the human mind, psychology, theology, and science, based on conscientious experimentation with psychedelics. One leading idea of Richards's study is that psychedelics tend to be wrongly conceptualized by taking for granted notions about an entity that is actually a cluster of enigmas: human mind or consciousness. Another leading idea is that psychedelic experiences, when responsibly experimented and dealt with, can help us gain more insights about the mind itself but also, and perhaps more importantly, increase or improve our psychological welfare, reducing depression, anxiety, and fear of pain and death, especially in the case of terminal illnesses. Such experimentation and subsequent study may also lead to therapies aimed at overcoming addictions and sociopathic personality disorders, he believes.

Richards's book is divided in five parts, each developed in three to five chapters. The first part reconstructs the history of psychedelic research, discussing as well the difficulties of choosing an appropriate vocabulary to conceptualize the substances in question and their effects. The second part expands upon mystical and visionary forms of consciousness as they are referred to in religious discourse. The third part discusses the relieving effects of entheogens, especially on terminally ill patients. The fourth part discusses present and future applications of entheogens in medicine, education, and religion. The fifth part, drawing upon the previous ones, is an invitation to abandon preconceptions and fears about entheogens and enter into a new interdisciplinary paradigm of discussion, study, and implementation. In the clinical parts the author does not hesitate to include narratives both of personal experiences with psychedelics and on those related by persons he was very close to. In the parts about religious discourses, Richards embraces a “Perennialist” stance: world religions (the differences between which are determined or influenced by the specific circumstances in which they appeared) seemingly incorporate and express the same encounter and relationship with the “sacred” that one can attain through psychedelic substances. Some suggestions are more explicit and articulated, others more sketchy but nevertheless also deeply fascinating, such as those inspired by other authors who have taken up the discussion of entheogens. He suggests that Plato and Dante may have had psychedelic/mystic experiences, and that humans may value precious stones or non‐figurative artistic and architectural patterns (such as those of Islamic art) because they are reminiscent of experiences with the sacred. Classical music lovers like the author of the present review may especially appreciate the suggestion according to which works by Bach, Brahms, Mozart, and others qualify as, or possibly stem from, psychedelic experiences, as well as the playlist at the end of the book, based on Richards's own research at Johns Hopkins Bayview Medical Center with suggestions for music that can accompany such experiences.

Richards writes with great competence, open‐mindedness, and wit. This book is truly a milestone in the interdisciplinary discussion of psychedelics/entheogens. There are some minor irritations, such as the misspelling of Humphry's surname (xviii), and of the new religious movement Barquinha (163), and more importantly of the scientific names of the plants composing ayahuasca: to the best of my knowledge they are Banisteriopsis caapi and Psychotria viridis, not Bannesteriopsis and veridis (162–63). I gasped at the oversimplified claim that the pope of the Galileo affair and Aristotle “were in agreement that the Earth was flat” (204–06). This is in fact a misconception, and a notorious one, having long been refuted in scholarly studies on the history of science, since the Galileo affair was mainly about geocentrism (Church) versus heliocentrism (Galileo). The spherical shape of the Earth was suggested by Aristotle, among others, and accepted by the Catholic Church in Galileo's times, as the worldview of the aforementioned Dante well demonstrates.

Attentive readers will not fail to notice that from the outset Richards makes clear and repeated appeals to “responsibility” and “maturity” and that, while touching upon prospective scientific investigations, he refers to well‐designed, double‐blind experiments (23); that is, held to strictly scientific standards. In other words, while inviting his readership to reconsider and redesign conceptual and research boundaries, the author's feet remain solidly grounded in science. I therefore agree with G. William Barnard, author of the foreword, who praises the book as a “treasure” (xi) and adds that in Richards's work one can find “words of moderation, words of clarity, words of sanity” (xiv).

One has thus to understand that the author is being humble while claiming that he adopts a “meat and potatoes” approach (22). On the contrary, Richards explores the boundaries of language, and plays with subtle and sensitive concepts with great care and analytical skills, even when he expresses psychedelic experiences in a rather poetic fashion. His book can be described as a linguistic tightrope dance, or a graceful walk on the eggshells of words, that Richards skillfully performs after decades of intensive and meticulous training. In light of this observation, one should also read Richards's astute epilogue, entitled “A Concise Report of Insights from the Frontier Where Science and Spirituality Are Meeting” and beginning with the statement, “In case you had any doubts, God (or whatever your favorite noun for ultimate reality may be) is…” (211).

All this leads me to think of another “front” that Richards's monograph may perhaps have addressed or at least hinted at. His goal and concern seems mainly to convince the skeptical or rigid critics of psychedelics among scholars and perhaps authorities. However, whereas Richards definitely meets the huge conceptual challenges entailed by the subject he addresses, sustained by his competence and by reference to solid experimentation, one should not forget that religious discourse about psychedelics is not always in the hands of similarly wise and well‐informed authors, as a brief inspection of books, booklets, and websites by facilitators and “neo‐shamans” the world over can confirm. More often than not, emphatic and cursory references to Kuhnian “paradigm shifts” are simply used in the attempt to open the door to pseudoscience, creating discourses in which enthusiastic, individual testimonials of “healing” unduly replace well‐designed experimentation. Freedom of religious opinion is frequently and deceptively invoked in order to defend wrong ideas about substances that could actually be dispelled through sound science (when not by means of logic alone). The term “medicine” is often used with great ambiguity, while anti‐medicine is in fact promoted; i.e., the usage of “sacred” substances instead of established cures for well‐known diseases. An author like Richards is well aware of the risks of ambiguity and sloppiness caused by careless, ambiguous language as well as by the neglect of science proper. Other authors, especially interested in their own self‐promotion as facilitators, clumsily deal with those very problems or, in the worst case scenario, exploit ambiguity itself to create illusions and delusions of healing and self‐improvement. Psychedelic substances are not “magic bullets,” as Richards himself emphasizes (143). When writing about neurosciences, he explains that “to formulate and test new hypotheses, one, of course, must have done his or her homework and mastered the language and current conceptual frameworks of a particular academic discipline” (160). Hence, one would also like to see a discussion of entheogens focusing more explicitly on the unfortunate and rampant role of pseudoscience in confessional discourse.