An area of visual communication that might be classified as a "design failure" is the visual presentation of information about "prescription-only medicines" for patients. This information is provided on packaging, leaflets, brochures, labels and websites. The practical issue is that there are problems in convincing patients to take medicines appropriately and effectively. Some of the assumptions that underlie the development of visual information for patients could be incorrect. A visual rhetoric framework is applied to help this article answer two questions: (1) is the current visual information about medicines a "communication failure"? (2) can visual rhetoric be used as a framework to indicate failures? The results show that visual rhetoric can be used as a basis for describing communication failures, but it needs to be incorporated into a larger "visual argument" structure. "Visual rhetoric" should be augmented by "visual dialectic" (dialogues between commissioner and designer, and interactions between patient and artifact) and "visual logic" (fundamental visual relations). The analysis indicates that visual information about prescription-only medicines for patients is--in general--not optimal and can therefore be seen as a failure. Application of some of the visual rhetorical principles indicates possible ways forward. (Contains 8 figures.)