Low and high blood sugar levels are known problems in some people taking Coreg and can cause serious or even life-threatening complications. Prevention is the best treatment. Therefore, anyone taking Coreg should be aware that low blood sugar or high blood sugar levels are possibilities. They should know the signs and symptoms of each and know what to do if these symptoms occur. If you have diabetes, your healthcare provider may also recommend that you check your blood sugar levels more frequently, especially when first starting Coreg or changing the dosage.