Metformin belongs to hypoglycemic drugs, blood sugar 8mmol/L can take metformin, but need to be under the guidance of a doctor. Metformin can reduce hepatic glucose production, inhibit the intestinal absorption of glucose, and improve insulin sensitivity by increasing peripheral uptake and utilization of glucose, applicable to type 2 diabetes mellitus that is ineffective in dietary and exercise treatments, and prohibited in type 1 diabetes mellitus, diabetic ketoacidosis, severe hepatic and renal insufficiency, etc. The drug needs to be used under the guidance of a doctor. Blood sugar including fasting blood sugar and postprandial blood sugar, if the fasting blood sugar or postprandial blood sugar 8mmol / L, need to consult a doctor in time, improve the oral glucose tolerance test and other tests, under the guidance of the doctor to clarify the diagnosis and use of medication, can not take metformin without authorization.