Ideally, supply-side drug control policies intend to create illegal drug scarcities that drive up illegal drug prices, and reduce purity levels to the extent that the price drug consumers pay is either cost prohibitive, or not worth the low purity product they have purchased. It is theorized that drug consumers will either seek treatment for their addiction, or stop using altogether. This theory has never panned out, yet supply side approaches remain the most resilient model of drug control policy in the United States. The American-led war on drugs is consistently framed through a domestic/ foreign polarity that is operationalized though tropes of criminality, suspicious narratives of foreign others, and the 'us vs. them' duality. The United States situates its drug control crusade as a matter of national security, where the expansion of the United States policing role underwrites drug enforcement activities in foreign nations as a regional security imperative. This dissertation is about the effects produced by the barriers of drug enforcement--the laws that behave as barriers, surveillance as a barrier, and the US-Mexico border fence as a barrier. These barriers produce unintended effects, creating new geographies of risk that emerge where these barriers are sited. Three case studies analyze these barrier effects--the human cost of surveillance practices that ultimately relocate drug supply routes, with devastating consequences; the unintended outcomes of legal mandates limiting access to prescription drugs and the shift toward riskier illicit substitutes; and faith that a border separation barrier will stop illicit flows of migrants and drugs, and the folly of believing these flows are intimately connected. This project is based on interviews with public health and safety stakeholders, document analysis of US federal narcotics court cases, content analysis of government reports, and analysis of United States Drug Enforcement Administration incident, seizure, price and purity data. In my research, I am interested in why path-dependent drug policy approaches are consistently adhered to, despite the inevitable geographic shifts and human consequences these decisions inevitably reproduce.