Many contemporary public health campaigns use some form of metaphor. Studies into what makes this strategy effective typically focus on the ability of metaphors to attract attention and trigger conversations. Consequently, the question of how they might enhance or impede people’s understanding of the information conveyed is often overlooked. This article brings together key concepts in Conceptual Metaphor Theory with the latest findings in health communication to present a framework for describing metaphors in health promotion on the basis of their experiential, internal, external and narrative coherence. Using the comparative analysis of two children’s comics about tuberculosis as a small-scale case study, the paper argues that metaphor coherence is particularly important in health campaigns that aim to convey complex, new information. The paper ends with suggestions for validating the framework more broadly.