Leary's promotion of LSD and his experiments with the drug at Harvard led to conflicts with the university administration and legal authorities. He was eventually dismissed from Harvard, and LSD was classified as a Schedule I controlled substance in the United States in 1965, making it illegal.
After being dismissed from Harvard, Leary continued to promote LSD and other psychedelic substances. He traveled extensively and engaged in international activities related to drug advocacy. He was arrested on multiple occasions for drug-related offenses. In court, Leary gave his occupation as "president of a religious organization-- the League of Spiritual Discovery, which communes by means of LSD, peyote, and marijuana--and he promptly began to proselytize.
"The United States is an insane asylum. LSD is the only solution for a world facing warfare and rioting," he told reporters. "In ten years," he prophesized, "20 to 30 million Americans will be using LSD regularly."
Leary's ideas and advocacy had a significant impact on the 1960s counterculture movement. He was seen as a guru of sorts, and his ideas about expanding consciousness and rejecting conventional values resonated with many young people of the era. His advocacy of LSD and other psychedelics left a lasting mark on the cultural and social movements of the 1960s and continues to be a topic of discussion and debate in the context of drug policy and the exploration of altered states of consciousness.