A comparative analysis of the use of psychoactive plants in northern Chile, specially San Pedro de Atacama and the Middle Loa and its tributaries (Caspana, Tocone, Lasane, Chiu-Chiu), with NW Argentina, as a probable diagnostic tool of shifting patterns of interaction. This work presents a review of the evidence for the ingestion of psychoactive plants in northeren Chile and NW Argentina with particular emphasis on chronology, iconography and modes of ingestion. The iconographic and stylistic differences, as well as the divergence in chroinology, suggests shifts in patterns of interaction between northern Chile and NW Argentina. Key words : Vilca, snuff, psychoactive plants, rapé