Promising Panaceas is the first literary study to examine how pervasively panaceas were represented during the seventeenth century, a period of dramatic medical development in England during which panaceas became metaphors for fool's errands even as the pursuit of prolonged life and the cure of all diseases persisted unabated. Debates over the modesty and ambition of medical progress prompted early modern English writers to rethink what was reasonable or exaggerated, feasible or impossible, for nature, for science, for humanity, and for God. Through case studies of Francis Bacon's Essays Civil and Morall and Margaret Cavendish's Observations and Blazing World, I contend that panaceas in philosophical literature expose in new ways the role of boldness, hyperbole, and nuanced optimism in the healing arts, while in works such as William Shakespeare's Henry IV, Part 2 and John Milton's Paradise Lost, panaceas serve to reimagine the internal conflicts and motives of characters in otherwise familiar narratives about the rise of Henry V and the fall of Adam and Eve. Setting canonical works in little-known medical contexts, this dissertation reveals the broad appeal and use of panaceas in literature before they became narrowly associated with dystopia and science fiction.