April 16, 1943: The hallucinogenic effects of LSD were (accidentally) discovered by Albert Hoffmann:

Well, the rest is just history. It wasn’t until the 60s that LSD was considered a “mind bending drug.” And it wasn’t until March 25, 1966 that LSD appeared on LIFE’s cover.

Hofmann became an employee of the pharmaceutical-chemical department of Sandoz Laboratories (now a subsidiary of Novartis), located in Basel as a co-worker with professor Jordan Jake, founder and director of the pharmaceutical department. He began studying the medicinal plant squill and the fungus ergot as part of a program to purify and synthesize active constituents for use as pharmaceuticals. His main contribution was to elucidate the chemical structure of the common nucleus of Scilla glycosides (an active principal of Mediterranean Squill). While researching lysergic acid derivatives, Hofmann first synthesized LSD on November 16, 1938. The main intention of the synthesis was to obtain a respiratory and circulatory stimulant (an analeptic) with no effects on the uterus in analogy to nikethamide (which is also a diethylamide) by introducing this moiety to lysergic acid. It was set aside for five years, until April 16, 1943, when Hofmann decided to reexamine it. While re-synthesizing LSD, he accidentally absorbed a small quantity through his fingertips and fortuitously discovered its powerful effects. He described what he felt as being:

… affected by a remarkable restlessness, combined with a slight dizziness. At home I lay down and sank into a not unpleasant intoxicated-like condition, characterized by an extremely stimulated imagination. In a dreamlike state, 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 colors. After some two hours this condition faded away.

This animated short, “The Bicycle Ride,” is a
fanciful depiction of Dr. Albert Hofmann’s discovery of LSD. This cartoon was debuted
at the “LSD Symposium” held in honor of Albert Hofmann’s 100th birthday in Basel, Switzerland.

This animation is loosely based on the account written by Dr. Hofmann himself in his, “LSD My Problem child”. The preceding link leads to the entire text online. See Chapter 1.4 for an account of LSD’s “discovery.”