For the Matsigenka of the Peruvian Amazon, health and well-being in daily life depend upon harmonious relationships within the social group and with the spirit world. Psychoactive plants play a crucial role in curing disrupted social relationships while giving humans access to the otherwise remote, parallel world of spirits. Different species and cultivars of psychoactive plants, as well as varying admixtures and doses, are used to obtain different intensities and qualities of psychoactive experience, depending upon the individual's goals. Strongly psychoactive plants are used by shamans to travel to the realm of spirits. A number of mild to strongly psychoactive plants are used by male hunters to put their souls and improve their aim. Mildly psychoactive plants are used to improve women's concentration for spinning and weaving cotton, to control negative emotions such as grief and anger, to manipulate the content of dreams, and to pacify sick or frightened children. A majority of such remedies come from the botanical families of Rubiaceae, Solanaceae and Cyperaceae, known sources of psychoactive compounds. Interdisciplinary research into the culture, botany and pharmacology of psychoactive plants in indigenous medical systems contributes to a better understanding of the role of psychological states in human health and well-being. Keywords : Amazonia, ethnopharmacology, ethnopsychiatry, materia medica, psychoactive plants, shamanism