Treatment costs are a major barrier to therapeutic adherence, especially in contexts of socioeconomic vulnerability. However, clinical communication on this topic remains limited. This study presents a scoping review and proposes the CUSTO model — Comprehend, Use accessible language, Seek preferences, Try alternatives, and Organize follow-up — as a practical tool to support healthcare professionals in addressing treatment costs sensitively and effectively. The review analyzed studies linking clinical communication and adherence, with emphasis on vulnerable populations. The proposal is also based on the authors’ experience in Brazil’s Family Health Strategy (SUS), in regions marked by poverty and low health literacy. The model aims to improve adherence, promote equity, and foster shared decision-making.