Lisinopril warnings. If you take medication or insulin to treat diabetes, track your blood sugar carefully while also taking lisinopril, particularly during the first month of its use. The combination of these diabetes drugs can cause a drop in your blood sugar levels. It’s also important to be aware of any signs of infection, such as a sore throat or fever, which could indicate problems with your white blood cell count. Before starting on lisinopril, be sure to let your doctor know if you have any type of surgery planned, including dental surgery.