By John Walsh

It's the psychedelic drug that inspired Hendrix and The Beatles - and shaped the music, art and literature of a generation.

It was known as acid, blotter acid, window pane, dots, tickets and mellow yellow. It was sold on the street in capsules and tablets but most often in liquid form, usually absorbed on to a piece of blotting paper divided into several squares: one drop, or "dot", per square. Lysergic acid diethylamide, or C20H25N30 to give it its snappy chemical formula, derived from lysergic acid, and it introduced you to a world of cosmic harmony and all-embracing love, or a black schizoid hell of paranoia and screaming demons.

The letters LSD once denoted English money in pre-decimalization days: librae, solidi, denarii, the Latin forms of pounds, shillings and pence. From the mid-1960s, however, the letters had only one meaning: they stood for the most powerful mood-altering drug in the world.

Those who experienced the 12-hour "trip" it engendered would report back with all the fervor and awe of travelers returned from mystic lands, desperate to relay the sights and sounds of their wild adventures, but frustrated by the impossibility of making their listeners see or understand their experiences. Sometimes, they'd been on a physical journey (usually no further than the garden or local shops); but mentally, the trip had taken them into a new realm of consciousness that was a) hard to evoke and b) very boring to listen to. They talked about the blinding sensory enhancement, and the synaesthesia of hearing colors and smelling the stars. They saw profound truths in cracks in the pavement and cosmic harmonies in a match flame. They tended to mention God, several times. The man who invented the stuff had a lot to answer for. He was a Swiss chemist called Albert Hoffman, and he died on Tuesday morning.

The fact that he reached the age of 102 seems a tribute to the efficacy of his invention. But its importance to the 20th century isn't as a therapeutic medical treatment. It may have altered some lives for the better, but its real importance is cultural. For LSD gave the Sixties a brand-new concept to embrace and apply to every area of life, especially the arts: psychedelia. The word was spelt wrongly – it should, strictly, be psychodelia – but its meaning was clear. It meant the making-visible of the soul: opening up your inner, half-glimpsed metaphysical self for inspection while in a state of profound relaxation and pleasure.

The English writer Aldous Huxley had, of course, been there years before, when he experimented with mescaline in the early 1950s. His 1954 book, The Doors of Perception (the title is taken from William Blake – "If the doors of perception were cleansed every thing would appear to man as it is, infinite") argued that altered-state-inducing drugs were good for you, if you were sufficiently clever.

"To be shaken out of the ruts of ordinary perception, to be shown for a few timeless hours the outer and inner world, not as they appear to an animal obsessed with survival or to a human being obsessed with words and notions, but as they are apprehended, directly and unconditionally, by the Mind at Large – this is an experience of inestimable value to everyone and especially to the intellectual," he said. But LSD was, by 1968, becoming available to all, and seemed, for a time, a thing that could change the world.

In theory, the entire young "counterculture" of the West, the same young people who listened to rock'n'roll, smoked dope, rejected the values of their straight, bourgeois parents and demonstrated against the Vietnam War, could all drop acid, discover their transcendent inner being, forsake their redundant ego and refuse to cooperate with the ordinary forms of society. They could, in the immortal phrase of Timothy Leary, LSD's greatest fan and most articulate zealot, "Turn on, tune in and drop out."

They could share with each other soul-perceptions that were denied to the straights, the military-industrial complex, the politicians and judges.... It didn't happen. But, for a few years, it felt as if the doors of perception might budge an inch.

The first acid trip was on 16 April 1943. It was an accident. Dr Hoffman had been conducting experiments with LSD-25, which he had synthesized from lysergic acid in 1938 and was trying to make again, having a "presentiment" that it could possess "properties other than those established in the first investigations". The doctor got some of the stuff on his fingers. In the afternoon he felt dizzy, couldn't work, went home to bed and wrote later that he entered a dream-like state. Behind his closed eyes, he saw streams of "fantastic pictures, extraordinary shapes with intense, kaleidoscopic play of colors" for a whole two hours.

Three days later, with a Dr Jekyll-like foreboding, he put himself through a guinea-pig experiment. He took 250mg (a colossal dose by blotting-paper standards) and went for a bicycle ride. Wherever he looked, the landscape became distorted as if seen through a funfair mirror. Though he was moving fast he felt completely stationary, as though the fields were whizzing by him.

Back home, he experienced the world's first bad trip. He became convinced that he was possessed by a demon, that his neighbor was a witch and that his furniture was trying to kill him. The doctor was summoned, found nothing wrong beyond a dilation of the pupils, and packed him off to bed. Hoffman's panic subsided and he started to enjoy the visions and exploding colors, the shifting kaleidoscope of shapes breaking up and folding into themselves. Every noise from the street became a visual event.

He woke next day full of beans, refreshed, reborn. His breakfast tasted delicious. In the garden, looking at birds and smelling the flowers, he described his senses as "vibrating in a condition of highest sensitivity, which persisted for the entire day".

"Bicycle Day", 19 April, was later commemorated by acid enthusiasts because it was the first conscious "trip" and it had had – just about – a happy ending. But the doors to perception are, for some truth-seekers, booby-trapped and dangerous. When LSD was co-opted by medical staff for recreational use, two decades after Hoffman's bike ride, users learnt the hard way how impossible it was to control the wild ride once it had started.

At Oxford in the early 1970s, we were frankly intimidated by the drug's reputation. We all wanted to try it, but were too chicken. The word in the quad was: if you had any secret hang-ups, mental instabilities, phobias, sexual inadequacies or social insecurities (the kind that surface in dreams,) you were wise of steer clear of acid. We knew when one of us was going to try it. "Tonight," I'd hear during dinner in hall, "Roger's tripping for the first time. But he'll have Will and Ollie with him, so he'll be OK."

I've always remembered Roger's first trip (so, I'll bet, has he). We all knew he'd be fine because he was so perfect: cool, handsome, easy-going, a hit with the girls, a dead ringer, with his corkscrewy curls, for Marc Bolan of T. Rex. And he was rich; he owned a Morgan, which he casually parked in the back quad. We knew Roger would survive the experience and bang on about it, like he banged on about his Bang and Olufsen state-of-the-art hi-fi. And anyway, Will and Olly would look after him.

The evening started well. The three students took a tab each, drank some wine and waited for results. An hour later, they were happily tripping on the college lawn, listening to the grass grow and hearing their voices transforming into harp notes. They went to Olly's room, smoked, listened to Tubular Bells in a haze of bliss. Then Roger went the gents. This proved a mistake.

After using the facilities, he washed his hands, dried them and looked in the mirror. Something caught his eye. He looked closer. Just below his cherubic lower lip, there was a spot. It's wasn't huge or septic, but it was unquestionably a skin eruption, a blemish. As he watched, it grew bigger and bigger until it took on the size and texture of a Brussels sprout. Roger was transfixed. He looked on in horror, as the distended spot grew wobblingly larger, and began to pull his features into its green heart. His nose disappeared, his cheeks and eyes began to twist down, his Marc Bolan curls hung uselessly over his aghast, imploding face.

Roger, you see, was indeed a near-perfect human being but he was as vain as a canary. And discovering a spot on his immaculate physiognomy played straight into his worst insecurity: that he might secretly be unattractive. He ended up imagining his whole head was a great blob of pus; and sat screaming with paranoia for two hours as his friends dosed him with orange juice (vitamin C is the only known cure for bad trips). Other occupants of his staircase, alerted by the noise, called in to discover a scenario straight from the locked unit of Bedlam hospital, circa 1880.

During the Cold War, both the British and the US governments were keen to exploit LSD's unique qualities, for "social engineering". They were convinced it would be useful as a "truth drug" during interrogations – a rather prosaic understanding of the kind of visionary truth revealed by communing with one's soul.

In 1953 and 1954, scientists working for MI6 drugged servicemen with LSD without telling them what to expect; the scientists told them they were looking for a cure for the common cold. One soldier, aged 19, reported that he saw "walls melting, cracks appearing in people's faces... eyes would run down cheeks, Salvador Dali-type faces... a flower would turn into a slug." Not surprisingly, the experiment failed; MI6 reported that LSD was of little practical use as a mind-control drug. It took 50 years for the human guinea-pigs to be compensated for what they'd been put through.

If LSD was no use in war, what was it good for? At first, the scientific community thought it could be a wonder drug to use in psychoanalysis, because it would help patients unblock repressed subconscious thoughts they couldn't unblock by other therapies; more than 2,000 research papers were written about the compound's possible applications.

At Harvard University in the early 1960s, the psychologists Timothy Leary and Richard Alpert set out to show that it could be used as a path to spiritual enlightenment, a catalyst to religious experience, a tool for accessing the divine; they preached their gospel all over America. As time went by, they seemed less and less like scientists, and progressively more like visionaries; Leary came on like a hippie, a guru, a slightly creepy uncle to the teenage students he was seeking to "turn on". By 1966, just as LSD was becoming established as the ultimate recreational drug, the US government lost patience with the mystical bullet, and banned it.

From that moment, it took off as symbol of the enlightenment that cops, governments and teachers didn't want you to experience. It was a holy drug that wasn't allowed near your tongue, no matter how much you craved communion with the cosmos. Instead of rebelling (that would come later) the counter-culture embraced the whole idea of LSD, and celebrated its effects in music, art, film, books, clothing, dance routines and in the floaty patterns of light-shows on walls.

Becoming stoned, murmuring "Wow, the colors, man..." while weaving across a roomful of acidheads listening to Pink Floyd's Piper at the Gates of Dawn – that was the UK version of psychedelia, the diluted legacy of Albert Hoffman's great discovery. Not that he regretted its checkered history. His book about the drug that turned the world inside out was titled LSD: My Problem Child.

The acid effect: LSD's influence on...

Movies

The definitive acid movie is The Trip, scripted by none other than Jack Nicholson, directed by Roger Corman and starring Easy Rider duo Peter Fonda and Dennis Hopper. Because it's wholly in favor of the acid experience (ad-man Fonda drops a tab and suffers nothing more than a swirly, psychedelic hallucination on the beach), it was refused a certificate by the censors. The LSD binge in Easy Rider, in which the boys celebrate their arrival in New Orleans by tripping with two hookers, features some vérité footage of Fonda enduring a real-life acid moment in a graveyard, wailing about his dead mother. The clash of violence and rock'n'roll, and the mingled identities of the lead characters in Performance, directed by Donald Cammell and Nicolas Roeg, is resolved when Mick Jagger and James Fox get weirded-out together on acid, and seem to enter each other's heads (shortly before a bullet enters Fox's.) Ten years later, in Altered States, Ken Russell attacked the enlightening powers of acid when he portrayed a psychedelically grooved-up William Hurt heading for perdition. Three decades after The Trip, LSD became a transformative magic spell in Irvine Welsh's 1998 film The Acid House (where a single tab makes a Hibs hardnut swap personalities with a yuppie infant) and a terrible means of torture in Dead Man's Shoes, as Paddy Considine feeds bad-trip acid tablets to the horrible men who made his brother hang himself.

Music

The combination of flower power and hallucinogenic drugs in Haight-Ashbury in 1967 was as potent as gunpowder and matches. Rockers who'd tried the big blotting-paper experience strove to replicate it in performances that were floaty, spacey, woozy and seemingly without beginning or end. The result was called acid rock: it was supposed to suggest the album had been recorded by a band in the grip of LSD, and was to be listened to by fans similarly stimulated. Lyrics were often minimal, and the sound often relied on randomly wacky special effects, complemented, during live shows, by a light show of wiggly patterns playing against a wall.

The Grateful Dead, from San Francisco's Bay Area, were the key US acid rock band; their leader, Jerry Garcia, a portly figure with a prodigious beard, could spin out the solo on "Dark Star" for 25 minutes. Jefferson Airplane also hailed from San Francisco and defined acid rock in 1967 with their album, Surrealistic Pillow. It featured "White Rabbit," which sneakily refers to the apparent drug consumption in Alice's Adventures in Wonderland and ends on the line: "Remember what the Dormouse said: Feed your head, Feed your head." Elsewhere The Doors drew their name from Aldous Huxley's book, and their leader Jim Morrison sang "The End" and "Riders on the Storm" in a blurry, reflective drone, like one intensely drugged.

In the UK, 1967 was the year of The Beatles' masterpiece, Sergeant Pepper's Lonely Hearts Club Band, whose early highlight was an hallucinogenic vision of tangerine trees and marmalade skies called "Lucy in the Sky with Diamonds". The capitalized letters seemed a dead giveaway, but Paul McCartney always denied it was a song about LSD. He later revealed that he'd tried the hallucinogenic, and is thought to be the person who first introduced it to Bob Dylan. The pre-eminent UK acid band was Pink Floyd in the days of Syd Barrett and The Piper at the Gates of Dawn. Their song titles took their cue from space travel – "Astronomy Domine", "Interstellar Overdrive" – as did the Rolling Stones in their single burst of psychedelia, "2000 Light Years From Home".

Because of the fundamental difficulty (pace Aldous Huxley) of evoking an acid trip in any meaningful way, the literature of LSD is limited. Heroin, cocaine, marijuana and alcohol may inform The Man with the Golden Arm, Bright Lights, Big City, Junky and The Lost Weekend, but the acid trip has proved elusive to prose. Perhaps the most notable literary "trip" was indeed a genuine trip: the journey taken by Ken Kesey and the Merry Pranksters in 1964 in a psychedelically painted school bus called "Further". The pranksters included Neal Cassady, Sandy Lehmann-Haupt, Stewart Brand, Carolyn Adams (the wife of Jerry Garcia) and two proto-hippies called Wavy Gravy and The Cadaverous Cowboy. They rolled east to New York, giving out tabs of acid to strangers, and were immortalized in Tom Wolfe's The Electric Kool-Aid Acid Test. It was that kinda time – when, in the words of William Burroughs, "a tiny psychoactive molecule affected almost every aspect of Western life".

Design

Swirling shapes, paisley patterns, surreally "fat" lettering, howlingly discordant but vivid colors and lots of strobe effects were the characteristic of acid art. The acid genre hardly lasted long enough to establish a niche in art history, but it enjoyed a considerable vogue in the world of posters. Between 1967 and 1972, there was hardly a "progressive" rock-gig poster that did not feature distorted lettering and swirly colors. Much of it was the work of Karl Ferris, a Hastings-born photographer who worked on the Psychedelic Happening shows of the mid-1960s, and, through them, met John Lennon, Paul McCartney, Graham Nash, Eric Clapton, T Rex and Pink Floyd. He brought his fish-eye lens and infrared color film to several classic LP covers, including the US versions of Hendrix's three albums, Donovan's A Gift from a Flower to a Garden and The Hollies' Evolution.

Elsewhere, the market was dominated by Hipgnosis, a British art design group made up of Storm Thorgerson and Aubrey Powell, who were responsible for the freaky early covers of Pink Floyd and Genesis. Other artists influenced by psychedelia include Victor Moscoso and Alan Aldridge.