The medicine skill is used to apply the potions made by biochemists to patients. Many of these potions can not simply be applied by anybody or just taken by the patent but rather require a trained expert to do so, which is the physician. If they are applied without a physician there is a high chance of negative consequences, so using a doctor is a good idea. There is a more specialized section that deals with this matter in depth.
(c) 2005, Sociolotronics LLC