Initial interest in the value of psychedelic drugs (“psychotomimetics") in psychiatry began in the early 20th century, with explorations of the possibility that mescaline or peyote could produce psychosis-like effects. Over time, interest was focused on whether the effects of psychedelics could inform as to the underlying basis for psychiatric disorders. As research contin­ ued, and especially after the discovery of LSD in 1943, increas­ ing interest in a role for psychedelics as adjuncts to psycho­ therapy began to evolve and became the major focus of work with psychedelics up to the present day.