It was the drug that fuelled the psychedelic 60s - and was tested as a weapon by MI6. But whatever became of LSD? Duncan Campbell traces its colourful past, and finds that the acidheads are still out there

'I was seeing what Adam had seen on the morning of his creation - the miracle, moment by moment, of naked existence ... flowers shining with their inner light and all but quivering under the pressure with which they were charged ... words like 'grace' and 'transfiguration' came to mind."

That was the writer Aldous Huxley extolling the benefits of LSD from his vantage point in the Hollywood Hills in 1953, and he remained, right up to his death - and possibly beyond - an admirer of the substance. He even took it on his deathbed in 1963 so that he could enter the afterlife with, as it were, his doors of perception wide open. Some of LSD's other proponents are still with us. Albert Hofmann, the biochemical researcher credited with discovering LSD in Switzerland in 1943 - he described it as his "problem child" - celebrated his 100th birthday in Basle last year. But where does LSD feature in the drugs firmament today?

This month sees the updated republication, after 20 years, of The Brotherhood of Eternal Love by David May and Stewart Tendler, the book that charted the history of the LSD counter-culture and the so-called Brotherhood that distributed it so energetically in the 60s and 70s. The book's epilogue brings us up to date with the surviving members of the tale.

LSD has certainly had a long, strange trip since it gained worldwide attention in the 60s. Timothy Leary, its most famous promoter, dropped out of his earthly existence in 1996 and his ashes were, appropriately enough, blasted into space. His book, The Politics of Ecstasy, still sells well and there have been reports in the past few months of plans for various feature films. One of them would involve Leonardo DiCaprio, who knew Leary and has always been interested in a life that involved espousing the drug, being busted, escaping from prison, holing up in Algeria and eventually ending up on the lecture circuit as a double-act with the Watergate burglar Gordon Liddy.

Augustus Stanley Owsley III, the San Francisco chemist who produced the famous "Owsley" dosages of LSD, is now in his 70s. He has long since left the production game and lives in Australia, where he sells jewellery, carvings and music from a website under his nickname, Bear. Owsley, described by US agents as "the man who did for LSD what Henry Ford did for the motorcar" and called "God's secret agent" by Leary, also writes essays on his website, still campaigning against the drugs laws and arguing that "the use of substances which alter in various ways the consciousness of man is an extremely ancient and established practice."

The Brotherhood of Eternal Love ran the drug's largest international network, stretching from California to Hawaii and Afghanistan, with a UK branch in the unlikely spot of Broadstairs, Kent. Described by the California department of justice as "a pseudo-religious organisation responsible for the manufacture and distribution of LSD on a worldwide level", it operated more or less with impunity between 1966 and 1971 and had an estimated 750 people involved before it came unstuck. Many of them ended up behind bars, but some are still out there, somewhere, hoping that the FBI has forgotten them.

Britain's best-known LSD network, which prompted what became known as Operation Julie, included a couple of doctors, two chemists, a teacher and an author. A total of 15 people were jailed for up to 13 years at Bristol crown court in 1978 after they were infiltrated by undercover police, some of whom inadvertently ingested some of the drug and had their own trippy experiences.

The drug also had a sinister sub-life within the intelligence world: the CIA experimented with it and even made an unsuccessful attempt to slip some into Fidel Castro's system before he made a TV broadcast. In Britain, in the 50s, servicemen were given the drug without being told, so that MI6 could study its effects. Last year, three of the servicemen received thousands of pounds in damages for being used as unwitting guinea pigs. One had described seeing, "Salvador Dali-style faces and cracks in people's faces". He had been told the tabs he was instructed to take were an attempt to find a cure for the common cold.

Officially, the production and use of LSD have diminished considerably since the days when psychedelia was fashionable, but there is still a strong underground market. "The interesting thing about LSD is that 20 years ago it cost £1.75 and it still costs about the same today," says Mike Jay, a trustee of the drugs policy foundation Transform and author of The Emperor of Dreams, a history of drugs in the 19th century. "It tends to be distributed now by enthusiasts rather than profiteers. It's an insider market and it's a seasonal thing. Every May or June, reasonably large amounts come in from California and Holland. The quality is quite good and it's not watered down as it was in the 70s and 80s."

"It is used much less than even a few years ago," says Matt McNamee of the drugs advice organisation Release. "People usually still put much more spiritual significance into it; they prepare for it in a way they don't with most other drugs." Users preferred the notion of taking LSD while "running across meadows with wildflowers" rather than ingesting it in a noisy club, he says. Dr Luke Mitcheson, a clinical psychologist with the South London and Maudsley NHS Trust, has just published with colleagues a study of hallucinogens among UK dance users. They noted that "the marked decline in LSD prevalence would seem very curious ... One possibility is that LSD's much longer duration is less compatible with leisure lifestyles that are organised around an evening out."

But there are still risks for anyone seeking to produce the drug, and dealing in it carries a 14-year jail sentence. In 2000, there was a spectacular bust in Kansas when William Pickard and Clyde Apperson were arrested by Drugs Enforcement Administration agents as they tried to move their mobile lab out of a grain silo. The agents claimed to have found 41.3 kilos (90lbs) of the drug - enough, they said, to make an estimated 10 million doses. But by 2004, a total of just 317,321 doses were seized worldwide. Seizures in this country are relatively tiny - around 7,000 doses in 2004, the last year for which figures are available. Jay reckons that well over 90% of the LSD trafficked around the world is below the radar of customs officers as it remains one of the easiest of drugs to smuggle, whether in liquid form - in, say, a nasal spray, or on blotting paper hidden in a book or wallet.

"I don't think that the Brotherhood had a beginning and I don't think that the Brotherhood had an end," says Nick Sand, one of the original bootleg chemists interviewed for the new edition of the book. "The Brotherhood exists. We are still brothers because we shared the light. The Brotherhood is still there between us. So has the Brotherhood died? No, of course not".

· The Brotherhood of Eternal Love by Stewart Tendler and David May is published by Cyan Books, price £11.99. To order a copy for £10.99 with free UK p&p go to theguardian.com/bookshop or call 0870 836 0875