René Descartes’s medical studies compose an important section of his entire production. Yet, both their incomplete and fragmentary nature, along with several other problems make medicine a secondary field in Descartes’s philosophy, despite the fact he depicted it as a branch of the tree of his philosophy. While historians of philosophy have generally downplayed its importance, several scholars have recently attempted to restore the centrality of medicine in Descartes’s philosophical enterprise. Yet, Descartes also provided medicine with a specific use. In this article, I aim to disclose his philosophical uses of medicine, as three medicines surface in Descartes’s work. The first is the physiology of vision in L’Homme, which Descarte...