Recent scholarship in medical humanities has expressed strong concern over the ability of pharmaceuticals companies to medicalize discomfort and subsequently invent diseases. In this article, I explore the clinical debates over the ontology of the sinus headache as a possible counter-case. Extending Foucault’s concept of principles or rarefaction, this paper documents the efforts of clinicians to resist the pharmaceutically-provided understanding of the sinus headache. In so doing, it offers institutions of rarefaction and rarefactive assemblages as useful heuristics for the exploration (...) of disease legitimization discourse. (shrink)