This is found with San Pedro using shamans, Ayahuasca drinkers in the Amazon, the Mazatec who use hallucinogenic mushrooms, and the Huichols who use Peyote (McKenna, 30). The key hallucinogenic alkaloid in the San Pedro cactus is mescaline.Mescaline is unique among drugs in that its main action is a stimulant of the visual and visuo-psychic areas of the cortex (Kluver, 65). This lets the brain experience an altered state of consciousness.n insightful article. on mescaline-containing cacti, including history and anthropology of. Huachuma (San Pedro) and Peyote cultural practices. author unknown. Western society has a negative view of hallucinogenic drugs and the psychedelic experiences that they produce.