Recent weaponized interdependence research has focused on mapping international economic structures to explain states’ capacity to inflict costs on foreign actors. This paper proposes a different approach that integrates weaponized interdependence research with microeconomic concepts of substitution. If an international economic exchange is restricted, actors on either end turn to the best available alternative. Substitution costs describe the utility loss actors incur when doing so. The extent of these costs determines whether either side can ‘weaponize’ the exchange.