This magic mushroom moment: a fan of funny fungi sorts fact from fantasy.

NOT LONG AGO, at a party in Amsterdam, I was about to swallow some psilocybin mushrooms when the host interceded. Dividing the pieces into two piles, he twirled a small metal ball hanging from a thin chain above each, dangled the same "dowsing" device over my hand, and after some contemplation pointed me to the pile that was right for me. He also predicted, using amazingly precise but unverifiable numbers, exactly how the mushrooms would affect me along several different personality dimensions. This ceremony, akin to an unsolicited palm, aura, or astrological chart reading, did not enhance my mushroom experience.

If you, like me, prefer your shrooms without the New Age baggage, Andy Letcher's Shroom: A Cultural History of the Magic Mushroom (HarperCollins) is for you. Letcher, a British writer and musician with a doctorate in ecology and another in religious/cultural studies, is careful to separate the truth about his subject from a "fantastical history ... dreamed up on the basis of wishful thinking and overworked evidence." Without dismissing the potential for mushroom-assisted mystical experiences, Letcher rejects the idea that psychoactive fungi inevitably lead people in a specific spiritual or ideological direction. At the same time, he scolds politicians for overreacting to a practice that poses minimal risks and brings much-needed "enchantment" to quotidian life.

Letcher emphasizes that the meaning of mushrooming, like that of other drug experiences, is "culturally contingent." In the 1960s, Americans and Europeans began actively seeking an experience they had until then equated with poisoning, reinterpreting effects that were once treated as signs of insanity or imminent death as an opportunity to explore inner worlds and see the outer one in a new light. Letcher's witty, entertaining, and surprising book tells the fascinating story of how this happened, chronicling the contributions of explorers, naturalists, mycologists, philosophers, authors, charlatans, rock musicians, and psychedelic visionaries.

Some of the facts Letcher confirms are at least as strange as the legends he debunks. Siberians, for instance, really do have a history of consuming fly agaric mushrooms not only directly but also "distilled via human kidneys." Letcher speculates that they discovered the psychoactive properties of the mushroom itself and the urine excreted by people who have eaten it by observing the antics of reindeer, who in the winter supplement their meager diet of lichen by lapping up human urine, presumably for its mineral content. In addition to the Siberian example, which goes back centuries at least, there is substantial archeological evidence that psilocybin mushroom use in Mexico and Central America, observed by Europeans at the time of the Spanish conquest, has been going on for thousands of years. Letcher notes that both the Siberians and the Aztecs used psychoactive mushrooms recreationally as well as for healing and prognostication.

But Letcher finds little or no evidence to support most of the too-good-to-check claims about the role of intoxicating mushrooms in human history. Do experiences with the fly agaric mushroom lie behind the legend of Santa Claus and his flying reindeer? Did witches, Druids, and whoever built Stonehenge partake? Was a fungus at the heart of early Christianity, Vedic soma rituals, and the Eleusinian mysteries of ancient Greece? Did prehistoric use of psilocybin mushrooms give birth to religion? Probably not, Letcher concludes, although in many cases the answer is unknowable.

Given the fly agaric mushroom's unpredictable psychoactivity and its unpleasant side effects (including nausea and twitching), it is remarkable that it figures so prominently in speculation of this sort, not to mention in children's stories such as Alice's Adventures in Wonderland and in fantasy writing for adults. Letcher suggests the fly agaric's fictional popularity can be traced largely to its distinctive appearance: red with white spots in a classic toadstool shape, perfect for fairy tale illustrations. The more user-friendly psilocybin mushrooms, which come from several species and take various shapes, do not have the same iconic form.

The main conclusion Letcher draws after sorting fact from fancy is that deliberate use of psychoactive mushrooms by Westerners is primarily a phenomenon of the last half-century. He argues that stories about ancient and momentous mushroom use can be understood mainly as attempts to validate a modern practice by giving it deep religious roots. In reality, he says, the magic mushroom moment is now, not some vaguely remembered time when a fungus-centered society lived in harmony with nature because it drew wisdom from a psychoactive sacrament.

It may be true that magic mushrooms have never been more popular, but they remain a distinctly minority taste. Even in Amsterdam, where psilocybin mushrooms are available over the counter in "smart shops," a 2001 survey found that less than 8 percent of the population had ever tried them, while only 0.3 percent had used them in the previous month. The risks this small minority runs, which include bad trips, accidents, and exacerbation of pre-existing psychological problems, hardly seem to justify the costs of prohibition. In fact, as Letcher notes, prohibition tends to increase the hazards to users by forcing them to rely on the black market, encouraging potentially deadly amateur mushroom hunting, and creating negative associations that make bad trips more likely. Around the time Letcher was wrapping up his book, the British government nevertheless closed a drug law loophole that had allowed possession and sale of fresh psilocybin mushrooms, a move he describes as "motivated more by political concerns than by any sensible assessment of the evidence."

A Labour Party M.P. objected to the hastily imposed ban. "We cannot make nature illegal," he said. "Magic mushrooms are part of the natural world. Some might describe them as a gift from God." If that sentiment sounds naive, how should we describe the attempt to purge the world of chemicals that produce politically incorrect states of consciousness, including chemicals contained in fungi that spontaneously pop up on cow patties and rotting wood all over the world? The mushrooms may not have magical powers, but neither do the prohibitionists.

Senior Editor Jacob Sullum ([e-mail]) is the author of Saying Yes: In Defense of Drug Use (Tarcher/Penguin).