The consolidation of antiretroviral therapy as the primary biomedical response to HIV infection in the global North has occasioned a growing interest in the health decision making of people living with HIV (PHAs). This interest is burdened by the weight of a behaviorist theoretical orientation that limits decision making to individual acts of rational choice. This article offers an alternative way to understand how PHAs come to take (or not take) biomedical treatments. Drawing on institutional ethnographic research conducted in Toronto, Canada, it explores how the "healthwork" of coming to take (or not take) treatments is organized by extended relations of biomedical knowledge. The article focuses on two aspects of the knowledge relations of coming to take pharmaceutical medications that transcend the conceptual and relational terrain of rational decision-making perspectives. First, it explores disjunctures between the everyday healthwork of poor, socially marginalized PHAs and the terms of biomedical decision making. Second, it investigates the knowledge-mediating activities of community-based organizations that help mitigate those disjunctures.