Metformin belongs to biguanide preparations, is a commonly used clinical oral hypoglycemic drugs, the mechanism of action of metformin is to promote the utilization of peripheral glucose, promote anaerobic enzymes, can improve insulin resistance, also help obese patients to control body weight. The common side effects of metformin mainly include the following: 1, gastrointestinal reactions, some patients taking metformin can appear epigastric discomfort, nausea, nausea, diarrhea and other gastrointestinal irritation symptoms, small doses to start, after meals can effectively improve the gastrointestinal tolerance. 2, lactic acidosis, metformin can promote anaerobic enzymolysis, resulting in increased lactic acid production, in patients with severe hypoxia, cardiopulmonary 3, allergic reactions, a small number of patients taking metformin may appear itchy skin, rash and other drug allergies. 4, hypoglycemia, metformin works by promoting the use of glucose, alone will not occur serious hypoglycemia, but when combined with insulin or other oral hypoglycemic drugs used at the same time, may also occur hypoglycemia, or even severe hypoglycemia.