Bicycle Day is an international holiday that commemorates the date that Dr. Albert Hofmann first tripped on LSD (Lysergic Acid Diethylamide-25) and bicycled home from his lab in Basel, Switzerland on April 19, 1943. Dr. Hofmann had synthesized several derivatives of ergot, a fungus found on rye, in the process of searching for new pharmaceuticals for Sandoz Laboratories. Dr. Hoffman first synthesized LSD-25 in 1938 but did not become aware of its psychedelic properties until April 16th, 1943 when he absorbed a small amount of the compound accidentally either through his fingertips or by ingesting it. Curious about the psychoactive effects, three days later he performed a self-experiment to determine the true effects of LSD, intentionally ingesting 250 micrograms, an amount he predicted to be a threshold dose (an actual threshold dose is 20 micrograms) on April 19th, 1943. He started to feel the effects and asked his laboratory assistant to escort him home. During the bicycle ride home, he experienced the psychedelic effects of LSD, making this the date of the first acid trip in history, propelling the West into the Psychedelic Age.
Article in Scientific American: Tripping in LSD’s Birthplace: A Story for “Bicycle Day” by John Horgan
Transcript from MindStates IV LSD Panel: Hypothesis on Albert Hofmann’s Famous 1943 “Bicycle Day” by David Nichol
Article on Erowid: High Holy Days by The Teafaerie
Article in academia.edu: Why Is Bicycle Day April 19th, not the 16th? by Tom Roberts