It did not take long for LSD to make the leap from experimental medical treatment to recreational drug. By the late 50s, the term psychedelic had been coined by the psychiatrist Humphry Osmond. He teamed up with Aldous Huxley and Al Hubbard, who ordered 43 cases of LSD from its maker, the pharmaceutical company Sandoz. They toured the US and Canada, preaching a way to the "other world" they found as their consciousnesses dissolved into kaleidoscopic visions.

The Beat writers Jack Kerouac, Allen Ginsberg and William S Burroughs all tried LSD, but it filtered down into the mass (or at least the middle-class) consciousness thanks largely to the mission of the Harvard professor Timothy Leary and his call for America to "turn on, tune in, drop out".

Meanwhile, the Office of Strategic Services (later the CIA) ordered the rest of the company's supply for a mind control drug programme called MK-Ultra, before manufacturing its own. The OSS's Operation Midnight Climax commandeered a San Francisco brothel so prostitutes could spike their clients.

Ken Kesey and his Merry Pranksters took the "Electric Kool-Aid Acid Test" and the drug became integral to the hippie movement's claim to be exploring (even liberating) the inner workings of the psyche and soul: LSD was the hallmark of San Francisco's summer of love in 1967 and its echoes in Notting Hill and Amsterdam. Everyone knew what the Beatles' Lucy in the Sky with Diamonds was about, and acid rock included the inimitable music of the Grateful Dead.

But behind the romantic cult of LSD lay its casualties, excesses and bad trips - sometimes leading people to jump to their deaths from the heights Huxley and Leary claimed to have climbed. "The brown acid ... be warned on that one," boomed an announcement at Woodstock.

Psychedelic chemistry soon advanced, producing LSD's offspring - ecstasy and ketamine among them - to handsomely enrich those who make them.