Galen attempts to define the Timaeus as a medical resource to justify medicine’s right to comment on issues regarding the soul and the nature of life, to which philosophers had long laid claim. I call attention to Galen’s commentary On the Medical Statements in Plato’s Timaeus and the Arabo-Latin prologue to the Synopsis of Plato’s Timaeus to illustrate how his assertions that the dialogue contains ‘medical’ information allow him to draw more expansive boundaries for medicine. My analyses of On the Doctrines of Hippocrates and Plato and The Faculties of the Soul Follow the Mixtures of the Body reveal that Galen advances more monopolistic claims on the soul for medicine by appealing to his anatomical expertise and the dialogue's link between bodily and psychic disease to show the pertinence of his medical expertise to psychological controversies and ethics. I conclude with a discussion of Galen's interpretation of the Timaeus' account of vegetative sensation, which posits a homology between plants and humans that he exploits to extend medicine's boundaries beyond the world of the body.