This article examines the regulation of nonsteroidal anti-inflammatory drugs, with particular focus on products approved for marketing in the United Kingdom, while denied marketing approval in the United States on safety grounds, and then subsequently withdrawn from the UK market on those grounds. Using international comparison of regulatory data never before accessed outside government and companies, together with interviews with relevant industry scientists and regulators, the article demonstrates the importance of regulatory expectations, deficits and paradigms. It is argued both that (...) these sociological concepts can be enriched by their application to detailed comparative case study of regulatory science, and that they provide an important policy-relevant framework with which to understand discrepant drug regulatory processes in a sociohistorical context. It is found that regulatory expectations and paradigms may be regarded as mediating factors between political culture and structural interests, on the one hand, and the outcomes of regulatory science, on the other. (shrink)