Morning fasting blood glucose 12mmol/l, how long to take glucose-lowering drugs to take effect there is no fixed time. If you are taking rosiglitazone, it usually starts after 15 minutes; if you are taking glimepiride, it usually starts after 20-30 minutes. Morning fasting blood sugar 12mmol/l belongs to high blood sugar, patients need to follow the doctor’s advice to take hypoglycemic drugs treatment. There are many types of hypoglycemic drugs, and each drug has a different onset of action. If you are taking rosiglitazone, usually about 10 minutes after the drug blood concentration rises, the drug began to play a role. If you are taking a drug such as glimepiride, it usually takes 20 to 30 minutes for the drug to start working. For diabetic patients, the medication should be used under the guidance of a doctor to avoid reducing or increasing the dosage on their own.