The article presents the analysis of a judicial case in the Ecuadorian Amazon. A recognized ancestral medicine practitioner, the shaman or uwishin (in shuar language), was sanctioned for the crime of homicide for the death of a participant in an ayahuasca ceremony or Natemamu Ritual. An analysis of the judicial process discourse accounts for the epistemic injustice of ancestral medicine and its practitioners; their lex artis is judicially analyzed with motivations plagued by stereotypes. This is a judicial case that shows the situation of the plurality of medicines against the criminal legal monism of the State. Ancestral medicine is in a situation of epistemic disadvantage that affects the interpretation of knowledge; we observe that judicial decisions are governed by a monocultural and stereotyped vision about shamans and the ayahuasca ritual, which leads to difficulties in the interpretation of the facts, the profession of the shaman and his lex artis, the applicable norms, affecting the principle of impartiality in the administration of justice, and the ineffectiveness of the principle of intercultural interpretation in criminal proceedings. Keywords: Epistemic injustice; epistemicide; intercultural justice; shamanism; ancestral medicine.