Western psychotherapy and indigenous shamanic healing systems have both used psychoactive drugs or plants for healing and obtaining knowledge (called "diagnosis" or "divination" respectively). While there crucial similarities between psychedelic- assisted psychotherapy and shamanic healing with hallucinogenic plants, there profound differences in the underlying worldview and conceptions of reality. Four paradigms are reviewed : ( I ) psychedelic psychotherapy within the standard Western paradigm-where the drug is used to amplify and intensify the processes of intellectual self-analysis and self-understanding; (2) shamanic rituals of healing and divination, which involve primarily the shaman or healer taking the medicine in order to be able to "see" the causes of illness and know what kind of remedy to apply; (3) syncretic folk religious ceremonies, in which the focus seems to be a kind of community bonding and celebratory workship; and (4) the "hybrid shamanic therapeutic rituals," which incorporate some features of the past two traditions. There two points in which the worldview of the shamanic and hybrid shamanic ceremonies differs radically from the accepted Western worldview : ( I ) the belief and assumption (really, perception) that the multiple realities ("worlds") that can be explored in expanded states of consciousness; and (2) the belief that "spirits," the beings one encounters in dreams and visions, are just as real as the physical organism. Keywords: hallucinogens, psychedelics, psychotherapy, shamanism, states of consciousness