April 19, 1943, Hoffmann performed a self-experiment to determine the true effects of LSD, intentionally ingesting 0.25 milligrams (250 micrograms) of the substance, an amount he predicted to be a threshold dose (an actual threshold dose is 20 micrograms).[7] Less than an hour later, Hofmann experienced sudden and intense changes in perception. He asked his laboratory assistant to escort him home and, as use of motor vehicles was prohibited because of wartime restrictions, they had to make the journey on a bicycle. On the way, Hoffman's condition rapidly deteriorated as he struggled with feelings of anxiety, alternating in his beliefs that the next-door neighbor was a malevolent witch, that he was going insane, and that the LSD had poisoned him. When the house doctor arrived, however, he could detect no physical abnormalities, save for a pair of incredibly dilated pupils. Hofmann was reassured, and soon his terror began to give way to a sense of good fortune and enjoyment, as he later wrote...

"... Little by little I could begin to enjoy the unprecedented colors and plays of shapes that persisted behind my closed eyes. Kaleidoscopic, fantastic images surged in on me, alternating, variegated, opening and then closing themselves in circles and spirals, exploding in colored fountains, rearranging and hybridizing themselves in constant flux ..."

The events of the first LSD trip, now known as “Bicycle Day”, after the bicycle ride home, proved to Hofmann that he had indeed made a significant discovery: a psychoactive substance with extraordinary potency, capable of causing significant shifts of consciousness in incredibly low doses. Hofmann foresaw the drug as a powerful psychiatric tool; because of its intense and introspective nature, he couldn’t imagine anyone using it recreationally -Wikipedia