The impact of adverse drug events (ADEs) on the cost and quality of health care today is indisputable. A significant portion of these events can be detected and prevented with computerized pharmacy decision support systems. Challenges to the successful implementation of decision support systems include availability and quality of patient data and the accessibility of drug information that can be integrated programmatically on a patient-specific basis. An additional related challenge is establishing the vocabulary (i.e., codes, terms, and meanings) to be used for the representation, exchange, and automation of drug information and clinical functions. A central argument of this article is that a concept-based medication vocabulary needs to be created in order to facilitate the development of pharmacy decision support. We address the medication vocabulary challenge by defining a specific concept-based model of drugs as the basis for a standardized medication terminology.