Metaphors can be used as crucial tools for reaching shared understanding, especially where an epistemic imbalance of knowledge is at stake. However, metaphors can also represent a risk in intercultural or cross-cultural interactions, namely in situations characterized by little or deficient common ground between interlocutors. In such cases, the use of metaphors can lead to misunderstandings and cause communicative breakdowns. The conditions defining when metaphors promote, and hinder understanding have not been analyzed in detail, especially in intracultural contexts. This study proposes an analysis of metaphors identified within an Italian corpus of diabetes care interviews. Through a coding scheme capturing the types and the probative weights of the linguistic evidence that can be used to detect misunderstandings, the communicative effectiveness of metaphors is indirectly assessed. The quantitative and qualitative analyses show a positive correlation between metaphor use and problematic understanding. A more detailed scrutiny of the interlocutors roles and topics of the metaphors points out that most of the problematic metaphors are used by patients, while most of the problematic ones used by providers concern non-clinical matters. These results can be explained as resulting from incorrect presumptions of common ground between the interlocutors.