For a Western observer, the idea of using a psychotropic drug to treat someone is inconceivable. This practice is nevertheless observed among the Shipibo-Conibo indigenous population in Western Amazonia and is explained by their particular cosmology. Most of the entities in the environment (trees, waterways, heavenly bodies) are considered as microcosms, populated by unique beings with specific knowledge such as the faculty of healing. In a mythical past, the Shipibo-Conibo could interact with these beings and benefit from their expertise, but today, they only catch sight of them in dreams. Only the shamans know how to create these meetings by ingesting a hallucinogenic vine (ayahuasca) during rituals: since this psychotropic agent is considered to be dangerous, its use is subject to an initiation and strict limitations. A privileged vehicle in shamanic mediations, the ayahuasca allows alliances to be formed with the beings in their forest and, through them, the shamans can then respond to the needs of the members of their community. By detailing the discourse of the Shipibo-Conibo shamans, their shamanic learning and practices, this article describes a practical and regulated use of psychotropic drugs in an indigenous context and demonstrates how the Shipibo-Conibo do not consider shamanism as a marginal esoteric practice common concept in the West – but rather as an institution in continuity with all social practices. Keywords: Western Amazonia, Shipibo-Conibo, shamanism, cosmology, ayahuasca