In his search for a migraine cure, the Swiss chemist had synthesised a chemical compound in his laboratory at the Sandoz drug company in Basle. That Friday afternoon he began to experience unusual sensations and went home to lie down.
He soon entered a 'dreamlike state', which he recorded in a report to his co-worker a few days later. 'With eyes closed - I found the daylight to be unpleasantly glaring - I perceived an uninterrupted stream of fantastic pictures, extraordinary shapes with intense, kaleidoscopic play of colours.'
The chemical that he had synthesised was lysergic acid diethylamide - LSD - which had been absorbed through the skin of his fingers. Albert Hofmann had embarked on the first acid trip.
The following Monday, he decided to experiment on himself in a more scientifically controlled fashion. But he took a larger dose and was not prepared for the outcome. Cycling home he began to experience the feeling of being threatened. 'A demon had invaded me, had taken possession of my body, mind, and soul.'
He asked for milk from his neighbour, which he thought would be an antidote to the poisoning. He barely recognised her. 'She was no longer Mrs R, but rather a malevolent, insidious witch with a coloured mask.'
Dr Hofmann, who is now 87, vividly remembers that day half a century ago. 'That was a horrible, terrible, terrible experience. I had the feeling of being out of my body, of being insane, of having lost all connection with reality,' he told the Independent. His worst fear at the time was that he had permanently put himself into the realm of the insane.
In the event he recovered fully. One of the surprising aspects of taking LSD is that it produces no hangover. Dr Hofmann felt elated the morning after. 'Breakfast tasted delicious and gave me extraordinary pleasure. When I later walked out into the garden, in which the sun shone now after a spring rain, everything glistened and sparkled in a fresh light.' To this day, Dr Hofmann is convinced that LSD - his 'problem child' - could be used in clinical medicine, a role that the Sixties drug culture, which resulted in LSD's criminalisation, has thwarted. 'It should be legalised. It should be distributed to people who can make good use of it. It should be made available to the medical profession, like heroin or morphine. LSD should have the same status.'
Psychiatrists should be able to use the drug to open up the consciousness of patients who respond to no other treatment, he said. 'LSD is not addictive, it is not toxic. The danger with LSD is this very deep change in consciousness. It is a very deep experience; it can be beautiful, it can be
The problem with LSD and other hallucinogenic substances is that they are not 'integrated' into our culture in the way that, for instance, mescaline and magic mushrooms formed an important part of the religious ceremonies of earlier societies, especially in South America. 'We have integrated alcohol and tobacco, but we've not integrated the hallucinogens. The next step is that it should be put into the hands of the shamans of our time, that is the psychiatrists,' Dr Hofmann said.
'I think 50 years' experience with LSD is nothing. For a substance which exhibits such new and extraordinary properties you must have much longer. Most of the people who say it is terrible have no experience. We must see what the future brings and in the future it should be possible to study this substance properly.'
There have been several attempts to study LSD in clinical settings. Gordon Claridge, a lecturer in abnormal psychology at Oxford University, was one of the many researchers who more than 20 years ago gave LSD to volunteers in controlled experiments. He was interested in finding a useful 'model' for the psychosis suffered by schizophrenics.
'I'm convinced we had a model for schizophrenia,' he said. Unfortunately he was unable to follow up the initial findings because LSD was made illegal. 'I still believe that if one is looking for a drug that gives an insight into the psychotic state, LSD is better than most,' he said.
That belief is not universally accepted. Heather Ashton, professor of clinical psychopharmacology at Newcastle University, said that although LSD has helped scientists understand the brain a little more, there is no evidence that it is clinically useful. And there are cases of LSD inducing permanent psychosis. Another pharmacologist said that it would be impossible for LSD to receive ethical approval for human experiments.
Nevertheless, there are scientists working on LSD in test-tube experiments. These have shown that the drug works by blocking a certain type of receptor molecule on the surface of some brain cells. A key chemical messenger in the brain - called serotonin - binds to the receptor as part of the normal functioning of the nervous system. LSD interferes with this
Because serotonin is so universal in the animal kingdom, LSD can affect other organisms in strange ways. A cat on LSD will cower in front of a mouse; a fish will swim sideways; a spider on low doses will build perfectly webs but on higher doses will spin nothing but a mess.
George Aghajanian, professor of psychiatry and pharmacology at Yale University, is trying to find out how LSD works. He said that blocking the 5HT-2 receptors is common to all hallucinogenic drugs. A high concentration of nerve cells with these receptors occurs in the cerebral cortex of the brain, the outer area associated with higher intellectual functions.
Extremely small quantities of LSD can induce a trip. Professor Aghajanian said this is because the drug binds strongly to the 5HT-2 receptor molecule, much more so than other hallucinogenic compounds, such as mescaline, which have to be taken in relatively large doses to have an effect. Does he think there is a medical role for LSD? 'I don't know. It was never proven to have any clinical value,' he said.
But the man who started it all remains convinced that his discovery has potential. Dr Hofmann even holds out the prospect of a use outside medicine, but 'not yet,' he said. 'The next step is to use it in medicine so that we can study all the effects. Maybe in the future it could be integrated into our culture like alcohol.'
His problem child is 'too extraordinary and ambivalent'. Its beautiful effects, he said, are only matched by the ferocity of its dark side.