Bicycle Day is observed worldwide every April 19, commemorating the anniversary of Swiss chemist Albert Hofmann's intentional ingestion of 250 micrograms of LSD in 1943, which led to the first LSD trip. Hofmann had initially synthesized LSD in 1938 while researching lysergic acid derivatives, intending it as a central nervous system stimulant. After accidentally absorbing a small amount through his fingertips, he decided to re-synthesize and explore its effects further. The day is named Bicycle Day because Hofmann had to ride his bicycle home from his laboratory while under the influence of the drug. The celebration began in 1985, initiated by Thomas B. Roberts in DeKalb, Illinois, and is recognized in psychedelic communities as a day to honor the discovery of this potent psychoactive substance.