At the margins of the global scale-up of antiretroviral treatment for HIV, the Democratic Republic of the Congo has experienced severe regional stock-outs of essential medicines. Usually framed by global health actors as signs of technical, logistical, and professional deficiency, antiretroviral scarcity is -perhaps surprisingly -rarely considered to be an exceptional event. Attention to the local consequences of scarcity in the east of the country, however, suggests that stock-outs arise from far more than mere infrastructural failings. Drawing on an investigative ethnography conducted in the province of South Kivu between 2016 and 2018, this paper examines how stock-outs in the region have political functions rooted in the calculated denial of medicine to geopolitically significant communities and individuals. Informed by extant research the geopolitics of health, I begin by conceptually framing the geographical significance of stock-outs and locate in their origins and functions the discriminate use of scarcity as a biopolitical tool. Then, drawing on interviews and the analysis of previously unpublished and uncollated stock records, I demonstrate the technical and political origins of stock-outs at six dispensaries in the province. The supply of essential medicines, I argue, has become weaponised and their denial represents a strategic gambit for armed actors seeking territorial footholds in the region. Focusing on the cases of two out-of-stock towns in the south of the province, I then examine patients' agonising experiences of stock-outs, the poisoning and distortion of local moral economies that scarcity gives rise to, and the profoundly ambiguous transformations of therapeutic citizenship birthed by denial of treatment. I conclude by returning to the scale-up of antiretroviral treatment and review the critical avenues opened up for health geographers by a focus on the provisioning, scarcity, and denial of essential medicines.