He then took LSD hundreds of times, but regarded it as a powerful and potentially dangerous psychotropic drug that demanded respect. More important to him than the pleasures of the psychedelic experience was the drug’s value as a revelatory aid for contemplating and understanding what he saw as humanity’s oneness with nature. That perception, of union, which came to Dr. Hofmann as almost a religious epiphany while still a child, directed much of his personal and professional life.

“It happened on a May morning — I have forgotten the year — but I can still point to the exact spot where it occurred, on a forest path on Martinsberg above Baden,” he wrote in “LSD: My Problem Child.” “As I strolled through the freshly greened woods filled with bird song and lit up by the morning sun, all at once everything appeared in an uncommonly clear light.

“It shone with the most beautiful radiance, speaking to the heart, as though it wanted to encompass me in its majesty. I was filled with an indescribable sensation of joy, oneness and blissful security.”

He earned his Ph.D. there in 1929, when he was just 23. He then took a job with Sandoz Laboratories in Basel, attracted by a program there that sought to synthesize pharmacological compounds from medicinally important plants.

It was during his work on the ergot fungus, which grows in rye kernels, that he stumbled on LSD, accidentally ingesting a trace of the compound one Friday afternoon in April 1943. Soon he experienced an altered state of consciousness similar to the one he had experienced as a child.

On the following Monday, he deliberately swallowed a dose of LSD and rode his bicycle home as the effects of the drug overwhelmed him. That day, April 19, later became memorialized by LSD enthusiasts as “bicycle day.”