Hospitals with Coronavirus disease (COVID-19) demand surges at the onset of the pandemic report medication shortages, a worrisome phenomenon as inadequate medication supplies negatively affect patient outcomes. The popular press implicates a lack of raw ingredients and spikes in purchases but rigorous research is needed to more accurately identify shortage causes. We leverage a quasi-experimental design on IQVIA’s National Sales Perspectives data from 2018-2020 with a focus on medicines related to U.S. hospital-based COVID-19 treatment and a set of control medicines not used for COVID-19. We contribute to supply chain theory by empirically demonstrating that stockpiling among U.S. medical providers in the early phase of the pandemic accounts for the shortages. The buyers’ behavior results in concentration of the sales volume of COVID-19 medicines in the first two months of the pandemic. After these first two months, the sales volume of drugs for COVID-19 treatment decreases significantly despite a nationwide increase in COVID-19-related hospitalizations. An implication for manufacturers is that orders due to stockpiling by downstream buyers early on in a pandemic period should be discounted when predicting future demand. We also investigate another potential cause: expected price increases in the future. Counter to concerns that drug manufacturers would engage in price gouging behavior, we find no evidence of price inflation for these drugs. Our results are robust to numerous sensitivity checks and have implications for manufacturers, hospitals, and policymakers that may improve medicine supply resiliency against future threats.