On April 19, 1943 Dr. Hofmann intentionally ingested 250 µg of LSD, which he hypothesized would be a threshold dose, based on other ergot alkaloids. After ingesting the substance Hofmann was struggling to speak intelligibly and asked his laboratory assistant, who knew of the self-experiment, to escort him home on his bicycle, due to the lack of available vehicles during wartime restrictions. On the bicycle ride home, Hofmann's condition became more severe and in his journal he stated that everything in his field of vision wavered and was distorted, as if seen in a curved mirror.

Hofmann also stated that while riding on the bicycle, he had the sensation of being stationary, unable to move from where he was, despite the fact that he was moving very rapidly. Once Hofmann arrived safely home, he summoned a doctor and asked his neighbor for milk, believing it may help relieve the symptoms. Hofmann wrote that despite his delirious and bewildered condition, he was able to choose milk as a nonspecific antidote for poisoning.

Upon arriving the doctor could find no abnormal physical symptoms other than extremely dilated pupils. After spending several hours terrified that his body had been possessed by a demon, that his next door neighbor was a witch, and that his furniture was threatening him, Dr. Hofmann feared he had become completely insane. In his journal Hofmann said that the doctor saw no reason to prescribe medication and instead sent him to his bed.

At this time Hofmann said that the feelings of fear had started to give way to feelings of good fortune and gratitude, and that he was now enjoying the colors and plays of shapes that persisted behind his closed eyes. Hofmann mentions seeing "fantastic images" surging past him, alternating and opening and closing themselves into circles and spirals and finally exploding into colored fountains and then rearranging themselves in a constant flux. Hofmann mentions that during the condition every acoustic perception, such as the sound of a passing automobile, was transformed into optical perceptions.

Eventually Hofmann slept and upon awakening the next morning felt refreshed and clearheaded, though somewhat physically tired. He also stated that he had a sensation of well being and renewed life and that his breakfast tasted unusually delicious. Upon walking in his garden he remarked that all of his senses were "vibrating in a condition of highest sensitivity, which then persisted for the entire day".