One of the most important medical description of Peyote and its effects at the time was that of Juan De Cardenas. His work Problemas y Secretos Maravillosos de Las Indias, published in 1591, provided detailed information about peyote and its medicinal effects on the body and the mind. De Cardenas' report was also significant in that it discredited the explanation that supernatural forces were the only cause of visions from certain drugs. His description of the effect of peyote (and other plants) were biological in essence.
Source: Anderson, E. F. (1996). Peyote: The divine cactus. University of Arizona Press.