This paper describes a Human Factors Engineering approach to a medication use system in the context of a hospital medication CPOE project. It presents the results obtained from the organizational analysis and describes the variations in the distribution of tasks among actors in the medication use process, which depend on the organization of the work system. It then focuses on nurses' medication administration tasks including the preparation and update of pill dispensers. This situation may be characterized according to the distributed cognition framework. The high level organizational features have an impact on the quality and safety of the coordination and communication procedures that characterize medication preparation and administration by nurses.