The purpose of this dissertation is to examine the transformation of marijuana into a police issue in Rio de Janeiro in the 1940s and 1950s. In this process, the police force of Rio de Janeiro was a key actor, but not the only one. Police interventions on the sale and consumption of marijuana in the city were object of a daily negotiation and disputes in social interactions that involved other key actors: journalists, judicial operators, small marijuana sellers and a diversity of consumers. In order to investigate these interaction realms, the dissertation opts for a narrative strategy that privileges an integrated approach, based on three movements: first of all, it focuses on a series of journalistic campaigns that, in dialogue with the police force and judicial actors, resulted in the outline of a public order problem regarding marijuana consumption; secondly, it analyzes judicial debates about the limits of police intervention in a diversity of social interactions that included marijuana; finally, it develops an analysis of daily police action in heterogeneous urban consumption circuits.