Richard Rudgley's research shows that, throughout history, humans have always got high. But the drugs, argues Marek Kohn, don't matter as much as the people who take them
They tried war, they tried moral crusades, they tried just saying no; and now they're trying multiculturalism. After all these decades of zero tolerance, the effort to explain the Winter Olympic snowboard embarrassment as a cultural misunderstanding was rather sweet. In the old days, snowboarders would have been depicted as marijuana-crazed delinquents in urgent need of haircuts and alarm clocks. When one tested positive for cannabis at the recent Games, however, it was a quite different story. With their wild hats and woolly ways, snowboarders lent themselves to the implication that they were not deviants, but a sort of ethnic minority. It was as if they had trooped down from the mountains, oblivious to drug laws and the Western notion of punctuality. This was a conflict of values between a colourful tribe and the dominant Suit culture.

Publishers and authors face a dilemma similar to that of the snowboarders and the sports authorities. Drug books need to be respectable, and they also need to test positive. Some people want to buy drug books because they are worried, but many more, users and fellow travellers, want to have their lifestyles or their ideals affirmed. We have been here before, of course. A generation ago, the shelves were buzzing with a heady mixture of counter-cultural hucksterism and earnest attempts to offer sober counsel on the "drug problem".

Different as they were in tone, the two tendencies shared a basic moral posture. Taking their cue from the division between licit and illicit drugs, they divided illegal drug use into two forms. On the one hand was mindless doping, and on the other forms of drug taking with the potential to expand the mind. The former was regrettable, though frequently understandable as a response to alienation. The latter, from the odd whiff of cannabis to mind-bending 250-microgram doses of LSD, was felt to be a higher-minded pursuit in more ways than one. It was this that formed the basis of the drug culture's claims for legitimacy - though the word itself was not in the alternative vocabulary - and that spared sympathetic liberals from having to condemn all illegal drug use.

Among the most successful drug books of that era were Carlos Castaneda's tales of cacti, deserts and shamanic initiation. Marketed as the reports of a participant observer, they proliferated like magic mushrooms before being revealed as fiction. They are half forgotten today. Only older viewers would have appreciated the reference in an episode of The Simpsons in which Homer entered a separate reality after eating a hallucinogenic chilli pepper, guided by a coyote whose lines were spoken by Johnny Cash. But Castaneda may have been ahead of his time, if not outside it. He was the first drug writer to appreciate the power of indigenous peoples as a source of legitimation.

Today, the distinction between drug taking for pleasure and for expanding consciousness has evaporated. Ecstasy is recognised as its own reward, and psychedelic experience is just another part of the package. In his new Encyclopaedia of Psychoactive Substances (Little, Brown, pounds 18.99), Richard Rudgley observes that the term "psychedelic" has fallen out of favour. The new buzzword is "entheogenic". It comes from "en theos", "god within": taking an entheogen is like taking a god into oneself. Besides the reassuring echo of Christian communion, it is intended to evoke the idea of divine possession and shamanic transports.

As a taxonomic class, entheogens don't mix well with stimulants and depressants. Either you classify drugs by the effects they unarguably have - stimulating the central nervous system, inducing hallucinations, causing sleep and so on - or according to the cultural constructs built around them. Both approaches may be valid, but hybridising them is not. In the case of entheogens, it smacks of an attempt to trump medicine with religion. If you replace the term "hallucinogen" with "entheogen", but retain the other standard classes, you imply that divine possession and CNS stimulation are commensurable categories. And you're letting old Carlos in by the back door.

As well as getting the gods on its side, the term "entheogen" puts hallucinogens in touch with their heritage. It asserts their legitimacy by appeal to tradition. They are part of many traditional cultures, and so deserve respect according to the principles of multiculturalism. It worked for the snowboarders, it might work for drug books.

The entries in Rudgley's Encyclopaedia make it look as though there are as many drugs as there are drug cultures. Like modern agriculture, which uses only a fraction of the species that could serve as crops, modern drug taking only picks a handful of cards out of the deck. Rudgley's stern introductory disclaimer - "Ingestion of some of these substances may be harmful or even fatal" - applies to an astonishing range of species.

Generations of children learned about the soporific effects of lettuce at their mothers' knees, thanks to Beatrix Potter, but they weren't told about nutmeg, morning glory or scotch broom. The hippies who were inspired to smoke banana peel by Donovan's song "Mellow Yellow" were barking up the wrong tree. "I'm just mad about saffron" was the line they should have latched on to, though Rudgley warns that this spice can be lethal.

Occasionally he displays a credulous streak, as when he suggests that giraffes may have a hallucinogenic substance in their bone marrow. A little evidence for adaptive effects would be in order here, such as insects dropping stupefied to the ground after drawing giraffe blood, or carnivores reeling away in confusion - which would be considerable, given the combination of a hallucinogen and a close-up view of a giraffe.

Rudgley's ethnological credentials are sound, though, and he is now researching the ancient use of psychoactive plants at the Pitt Rivers Museum in Oxford. This book actually reveals less of his scholarship than its predecessor, The Alchemy of Culture: Intoxicants in Society (British Museum Press, pounds 14.95). There, for example, he notes the work of David Lewis-Williams, who has made intriguing comparisons between Southern African rock art and the Upper Palaeolithic cave art of France and Spain. In the Encyclopaedia, contextual information of this kind is limited by the way in which nearly all the entries refer to specific drugs.

Just as trainspotters mistakenly imagine that engines are the most interesting thing about railways, drug publishing is a sucker for the fallacy that drugs are the most interesting thing about drug taking. Rudgley himself is most fascinated by the kind of culture that induces Siberians to eat fly agaric mushrooms and then offer a drink of their urine to their grateful fellows. Taking the multicultural view, it's no odder than what Western athletes are expected to do with their urine samples.