Metformin is the first-line drug for type 2 diabetic patients to control hyperglycemia, and the application should pay attention to the contraindications. Firstly, it is not recommended for people with renal insufficiency, hepatic insufficiency, and those suffering from chronic gastrointestinal disease and chronic malnutrition. Second, type 1 diabetic patients cannot use metformin alone, but can be combined with insulin, which can reduce the amount of insulin and blood sugar fluctuations. In addition, type 2 diabetic patients who are combined with serious complications, acute complications, metabolic disorders, serious infections should not apply metformin, pregnant women and lactating women are not suitable for application. In addition, patients who are allergic to the drug or have serious adverse reactions, and people who are alcoholics should not apply metformin.