Insulin and metformin can generally be used together. The indications for insulin are diabetics who are poorly treated with oral medications, surgery, labor and delivery, and pregnancy. It is contraindicated in people who are allergic to insulin. Adverse reactions are mainly hypoglycemia. Metformin is indicated for type 2 diabetes mellitus, and can be used alone or in combination with other drugs; for type 1 diabetes mellitus, it can be used in combination with insulin to reduce insulin dosage. Contraindications are: hepatic and renal insufficiency, hypoxia and hyperthermia patients, allergy. Adverse reactions include lactic acidosis, nausea, abdominal distension, and skin allergy. Insulin and metformin, whether they are used at the same time, need to be based on blood glucose and the patient’s condition of comprehensive consideration, and used in accordance with medical advice.