The aim of this paper is to identify the prevalence of the most frequent drug interactions in patients using oral antidiabéticos and their association with capillary glucose and medication adherence. In total, 579 type 2 diabetes mellitus patients from 12 health institutions in Fortaleza, Brazil were interviewed in 2009. A form was applied, including questions on medication use, comorbidities, lifestyle, body mass index and random capillary glucose. Results revealed that 26.7% used five or more different drugs simultaneously and daily. Statistically significant drug interactions occurred between antidiabéticos and diuretics, angiotensin-converting enzyme inhibitors, anti-lipidaemics and corticoids. No significant association was found between polypharmacy, medication adherence and glucose. It is important for nurses, in consensus with other health professionals, to consider the possibility of other drugs that mean less risk for diabetes patients’ glucose control or of increased antidiabetics doses.