Over the next few years, he worked his way through the lysergic acid derivatives, eventually synthesizing LSD-25 for the first time in 1938. After minimal testing, LSD-25 was set aside as he continued with other derivatives. Four years later, on April 16, 1943, he re-synthesized LSD-25 because he felt he might have missed something the first time around. That day, he became the first human to experience the effects of LSD after accidentally ingesting a minute amount. Three days later, on April 19, 1943, he decided to verify his results by intentionally ingesting 250 ug of LSD. This day has become known as "Bicycle Day" as Hofmann experienced an incredible bicycle ride on his way home from the lab.