A Compound Shelved for Five Years
Albert Hofmann synthesized lysergic acid diethylamide — LSD-25, the 25th compound in a research series — in 1938 at Sandoz Laboratories in Basel, Switzerland, while searching for a circulatory stimulant derived from ergot fungus. It didn't show the effects he was looking for in animal testing, and Sandoz shelved it. Nobody ingested it. For five years, nobody did.
April 16, 1943: An Accident
On a Friday afternoon, Hofmann decided to resynthesize a small batch — he later wrote he had "a peculiar presentiment" about the compound, with no scientific reason given. During the synthesis he apparently absorbed a trace amount through his fingertips, left work early feeling dizzy, and lay down at home. What followed passed within a few hours, and by Monday he was back at work trying to figure out what had happened to him.
April 19, 1943: On Purpose
Suspecting the LSD-25 was responsible, Hofmann decided to test it on himself deliberately: 250 micrograms dissolved in water, taken at 4:20pm. It was, by his own later admission, a massive dose — he had no reference point yet for how potent the compound actually was. Effects arrived faster and harder than three days earlier. Within an hour he was too disoriented to keep working, and wartime restrictions on car use meant the only way home was by bicycle.
The Ride, and the Report He Actually Filed
This is the part people mean when they say "Bicycle Day": a ride home through Basel that Hofmann, in the account he published 36 years later in his memoir LSD: My Problem Child, described as giving way to a terrifying episode at home — convinced his neighbor was a malevolent witch, convinced the drug had poisoned him permanently — before the fear dissolved into something closer to wonder, with kaleidoscopic play of colors and a sense of rebirth by morning.
That's not quite what Hofmann told his boss at the time. The report he actually wrote on April 22, 1943 — three days later, to Professor Arthur Stoll, director of Sandoz's pharmaceutical department — described something closer to what he and the visiting doctor took for a massive overdose of amphetamines: dizziness, physical distress, fear of dying or going insane, and visual disturbances he characterized as unpleasant and in predominantly toxic-green and blue tones. The now-famous kaleidoscopic, fountain-like imagery doesn't appear in that report. It appears in the memoir, written in 1979, by which point Hofmann had three more decades of psychedelic culture's own vocabulary to describe it with.
Why It Became a Holiday Anyway
None of that makes the event less significant — Hofmann's self-experiment is still the first intentional LSD trip in recorded history, not the first exposure. Sandoz went on to market LSD-25 as a research tool for psychiatry under the name Delysid starting in 1947, and it remained a legitimate subject of clinical study for two decades before cultural and political backlash pushed it into Schedule I status in the US by 1970. April 19th has been informally marked as "Bicycle Day" since at least the 1980s, growing into an unofficial psychedelic-community holiday with no governing body and no single official event — just a shared anniversary, anchored to one extensively documented, messier-than-advertised Monday in Basel.
This is historical reporting, not an endorsement of unsupervised psychedelic use. LSD remains a Schedule I controlled substance in the US with no approved medical use outside clinical trials.