Psychedelic substances present in nature have been used by humans across hundreds of years to produce mind-altering changes in thought, mood, and perception-changes we do not experience otherwise except rarely in dreams, religious exaltation, or psychosis. U.S. scientists were studying the practical and therapeutic uses for hallucinogens, including LSD and mescaline, in the 1950s and 1960s supplied by large manufacturers including Sandoz. But the government took steps to ban all human consumption of hallucinogens, and thus the research. By the 1970s, all human testing was stopped. Medical concerns were not the issue, the ban was motivated by social concerns, not the least of which were created by legendary researcher Timothy Leary, a psychologist who advocated free use of hallucinogens by all who desired. Nationwide, however, a cadre of scholars and researchers has persisted in pushing the federal government to again allow human testing and the moratorium has been lifted. The FDA has begun approving hallucinogenic research using human subjects. In these groundbreaking volumes, top researchers explain the testing and research underway to use-under the guidance of a trained provider-psychedelic substances for better physical and mental health.