Drug development and pharmacotherapy are both governed by regulatory science, which involves “the development of new methods, standards and models we can use to speed the development, review, approval and ongoing oversight of medical products.” Drug safety is an important component of the US Food and Drug Administration (FDA) Strategic Priorities for 2011-2015 and the European Medicines Agency (EMA) Road Map to 2015, bearing witness to the intimate relationship between regulatory science and the science of safety. While both agencies share a paramount commitment to protecting and promoting the health of citizens under their jurisdiction, decisions in individual cases can differ, leading certain medicines to be available to citizens of some countries and not others. This paper presents two case studies illustrating a lack of harmony in respective regulatory landscapes.