San Pedro (Trichocereus/Echinopsis pachanoi) is a thin, columnar cactus native to the Andes mountains of South America, including countries like Peru, Chile, and Ecuador. It contains mescaline, a psychoactive alkaloid known for its potential to produce visionary and transformative experiences. Mescaline was the first substance classified as a "psychedelic" by Aldous Huxley, a pioneer in the field.