Metformin is a commonly used drug for diabetic patients, and it is recommended as the first-line drug for the treatment of diabetes in the guidelines of the Chinese Medical Association and the guidelines of many countries. It has the effects of improving insulin sensitivity, inhibiting glycogenolysis, reducing hepatic glucose output, and does not cause significant weight gain. Applicable people include: 1, patients with type 2 diabetes mellitus, especially those with obesity, overweight, hyperinsulinemia. 2.Using other oral hypoglycemic drugs or insulin alone, blood glucose control is not good, can be combined with metformin. 3.People with impaired glucose tolerance can choose to use metformin. In daily use, the possible adverse reactions are: the main side effects are gastrointestinal side effects, including nausea, vomiting, abdominal pain, abdominal distension, etc., mostly occurring in the early stage, but most of them can be tolerated. In addition, not all diabetic patients can use Metformin, the following groups of people are prohibited: diabetic ketoacidosis, hepatic and renal insufficiency (serum creatinine more than 1.5mg / dl), cardiac failure, serious infection and trauma, major surgery and clinical hypotension and hypoxia, alcoholism, vitamin B12, folic acid deficiencies, the combination of severe diabetic nephropathy, diabetic ophthalmic fundus lesions, Pregnant and lactating women. When using iodine-containing contrast medium for examination, it is recommended to stop using it for more than 24 hours, and then consider whether to resume it after 24 hours after the examination according to the situation, as it may lead to the deterioration of acute renal function (metformin itself does not harm the liver and kidneys, don’t listen to rumors).