In our era, the idea of a stimulant is synonymous with its biochemical properties. A stimulant, we think, is a substance that enhances the activity of the central and peripheral nervous systems. But in the eighteenth century, a new family of theories about the workings of stimulants took shape, based on exciting but erroneous assumptions. Proponents of these theories thought that many more diseases were "nervous" in origin than had previously been supposed. They hoped that the workings of the "nervous power" could be aided by the judicious use of stimulants and narcotics. Practitioners working within this broad "neuropathological" paradigm equated the workings of stimulation with those of gravity. Stimulation, they believed, was a kind of master principle in nature. Some hoped it would help refound medicine on Newtonian, mathematical lines. For patients, the most visible legacy of the neuropathological revolution was the abandonment of bloodletting or "cupping" and the increasingly widespread use of opium and alcohol in medical treatments. In this chapter, I explore the career of one of the most famous writers of the Romantic era, Samuel Taylor Coleridge (1772-1834) who had the misfortune to live through this therapeutic revolution. I describe the circumstances under which he came to take opiates and the development of his opinions about their effect on him.