Originally part of the Healers Guild, the Medics Guild became a distinct entity about fifty years ago, when the Last War was at its height. The armies of the Five Nations wanted healers who could march with them. As soon as the national armies demonstrated that they would pay handsomely for that privilege, House Jorasco started establishing mobile hospitals, relying on House Vadalis for sturdy draft animals and on House Deneith for military training. Like House Ghallanda’s Dragontail Guild of field provisioners, the Medics Guild has contracted somewhat now that the Last War is over. But House Jorasco has been more aggressive in finding new ways to put mobile healers to use. House Tharashk, for example, is increasingly hiring the Medics Guild to assist its dragonshard prospecting operations in the Shadow Marches, where diseases (and battle wounds, for that matter) run rampant.
Source: Eberron Campaign Guide