In a diabetic patient, what medication is most likely causing a 3-month persistent cough?

Lisinopril is an angiotensin-converting enzyme (ACE) inhibitor commonly used to manage hypertension and heart failure, and it is also indicated in diabetic patients for renal protection. A well-documented side effect of ACE inhibitors like Lisinopril is a persistent dry cough. This occurs due to the accumulation of bradykinin, a substance that is not adequately broken down when ACE is inhibited.

In this scenario, the patient's 3-month persistent cough is most likely attributed to the use of Lisinopril. While upper respiratory infections, walking pneumonia, and sinus infections can cause coughing, they typically do not result in a persistent cough over such an extended duration without accompanying symptoms like fever or malaise that usually would suggest an infectious cause. Thus, the chronic nature of the cough, especially in the context of a patient taking Lisinopril, supports that this medication is the most likely contributor to the observed symptom.