For better or worse, Albert Hofmann has a lot to answer for. It was Hofmann, a chemist working for Sandoz Laboratories in Switzerland, who in 1943, in search of a respiratory and circulatory stimulant, inadvertently hit upon a substance called lysergic acid diethylamide, or LSD. Accidentally ingesting some of the substance, Hofmann found himself overcome by ‘an uninterrupted stream of fantastic pictures, extraordinary shapes with intense, kaleidoscopic play of colors’. This was the world’s first acid trip.

It was Hofmann, too, who in 1958 isolated psilocybin, the ingredient found in several species of ‘magic mushrooms’ from Latin America. These had long been used in shamanic rituals, but Hofmann’s breakthrough allowed psilocybin to be easily prepared in the laboratory for clinicians and psychiatrists to use in ‘psychedelic therapy’.

This book by Michael Pollan, an acclaimed American author of a number of works on our relationship to food and nature, explores the history of both drugs. He examines how these became the launch pad for millions of hippy trips and, latterly, acquired (a sort of) respectability as a possible panacea for a range of psychiatric ills. It is at once a cultural history and an exploration of psychopharmacology, philosophy and mysticism.

As Pollan recounts, in the late 1950s and early 1960s psychedelics were initially welcomed for their possible therapeutic benefits. Cary Grant famously took more than sixty trips under the guidance of his California psychiatrist, declaring that, as a consequence, he could no longer behave untruthfully to anyone, ‘and certainly not to myself’ – adding, as a further incentive to anyone minded to try this approach, ‘young women have never before been so attracted to me’. The British clinical psychologist Humphry Osmond was among the first to use LSD with positive results in the treatment of alcoholism. Bill Wilson, the founder of Alcoholics Anonymous, himself took a couple of trips and was convinced that the drug could provide the spiritual awakening necessary to help alcoholics get sober.

It was Osmond who in 1953 had provided Aldous Huxley with mescaline. Huxley famously chronicled his experiences of the drug in The Doors of Perception, rhapsodising to Osmond that ‘people will think they are going mad, when in fact they are beginning, when they take it, to go sane.’ Huxley cautioned that psychedelics should be treated with care, but the genie came out of the bottle when Timothy Leary started hailing LSD as the sacrament of a new psychedelic religion. Stories about ‘wonder drugs’ gave way to lurid accounts of ‘bad trips’, psychotic episodes and people hurling themselves off buildings in the belief that they could fly. The moral panic that ensued led to the outlawing of LSD in America in 1966 (psilocybin was outlawed four years later). Sandoz withdrew the drug from the market, in the process shutting down more than seventy research programmes in existence at the time.

Research did not entirely stop, however. Self-styled ‘psychonauts’ continued to explore the effects of psychedelics, and in recent years legal research has picked up at a number of institutions in America and Britain. If the first generation of psychologists and psychiatrists generally viewed psychedelics in strictly clinical terms, the new generation seem more minded to blur the boundaries between science and religion, and to consider psychedelics as an entry to what the psychiatrist Charles Grob calls ‘the realm of applied mysticism’.

At Johns Hopkins Medical Center in Baltimore, researchers have guided and analysed more than three hundred psilocybin journeys. The descriptions are invariably the same – an impression of the self disintegrating and the development of intense feelings of love, benevolence and a sense of communion with the universe that respondents find impossible to convey in words. Tests involving people dying of cancer have shown significant reductions in anxiety and depression, along with a marked ‘existential reassurance’ that life – or at least consciousness – does not end with death.

Underpinning Pollan’s book is the thorny question of whether the psychedelic experience is purely a chemical reaction – mere ‘toxic delirium’, as one researcher puts it – or a doorway to the sort of spiritual or mystical experiences associated with saints and mystics over the ages. Do these experiences take place ‘inside’ the closed circuit of individual consciousness or are they, as many volunteers come to believe, genuinely from ‘out there’ or ‘beyond’?

Pollan goes into considerable detail about the effects of psychedelics on what scientists have identified as the default mode network (DMN), which is the part of the brain where our minds go to ruminate, reflect on ourselves and worry. The DMN appears to play a critical role in the creation of mental constructs or projections, the most important of which is the construct we call the self, or ego. Psychedelics appear to temporarily disable the DMN, causing the usual boundaries we experience between self and the world, subject and object, to melt away. Mystical experience, it seems, is simply what happens in the space that opens up in the mind when what Emerson described as ‘all mean egotism’ vanishes. Hinduism and Buddhism have been teaching this for millennia.

‘Set and setting’, as Leary observed, are a crucial element in determining the shape and outcome of the experience. Quiet surroundings and a supportive and experienced ‘guide’ are more conducive to a happy voyage than sitting in a muddy field at a rock festival listening to death metal. Expectations may also critically affect outcomes. Pollan argues that the fact that Huxley interpreted his experience with mescaline in terms that reflected his own interest in Eastern mysticism established a template of cultural expectation that Leary followed. Leary in turn set the template for ‘psychedelic orientalism’ with his book The Psychedelic Experience, based on the Tibetan Book of the Dead. (Leary emerged from one LSD trip at a Hindu ashram in Boston convinced that ‘we are all Hindus now’. But when Herman Kahn, an analyst for the RAND Corporation, took LSD as part of an investigation carried out by the psychiatrist Sidney Cohen, he claimed to have spent much of the session reviewing bombing strategies against China.)

Most engrossing are Pollan’s descriptions of his own experiences with psychedelics, by turns forensic and poetic, which read like the accounts of a traveller returning from a faraway and unfamiliar land – which in a sense they are. LSD takes him on a series of ‘encounters’ with his family that resemble ‘a cascading dam break of love’, in which ‘platitudes that wouldn’t seem out of place on a Hallmark card glow with the force of revealed truth. Love is everything’. Eating a magic mushroom, he is projected into something like a computer-generated world where the primary colours are black and grey. In the bathroom he pees ‘a waterfall of diamonds’ that seems to last ‘a pleasant eternity’.

Emboldened by these experiences, Pollan is persuaded to smoke vaporised toad venom, guided by a woman described to him as ‘probably the world’s leading expert on the toad’ – although, as he adds, ‘how intense, really, could the competition for that title be?’ Inhaling ‘the toad’, he finds himself rushing backward through fourteen billion years, watching the dimensions of reality collapse until there is nothing left, not even being. ‘It was just horrible.’

Driven to examine whether or not his own experiences qualify as ‘mystical’, Pollan, an atheist, concludes that – the toad notwithstanding – he understands for the first time what Emerson meant when he talked of being a ‘part or particle of God’. Tennyson’s observation of death being ‘an almost laughable impossibility’ now makes perfect sense.

Pollan has no doubt that the use of psychedelics could have a powerfully beneficial effect on a range of conditions, including depression, addictions and obsessions, and may even have a contribution to make to the development of a ‘grand unified theory’ of mental illness. For the moment, however, the prospect of ‘white coat Shamanism’, with psychedelic treatment centres and ‘board-qualified’ guides, might be some way off. As Pollan points out, there is little incentive for the pharmacological industry to manufacture psychedelics: if just one trip is enough to change someone’s life, there is unlikely to be a lot of repeat business.

This deeply absorbing, wise and beautifully written book makes an important contribution to the debate. As Pollan writes, the ‘great gift’ of psychedelics is to imbue everything in our field of experience with a heightened sense of purpose and consequence – ‘the making of new meanings, and the experience of awe.’ Just steer clear of the toad.