The most important side effects of metformin hydrochloride tablets are as follows: First, gastrointestinal reactions, metformin can cause poor nausea, vomiting, abdominal pain, diarrhea, metallic taste in the mouth and other gastrointestinal reactions, patients can take it after meals to reduce gastrointestinal irritation. Second, liver and kidney damage, when liver damage is obvious or combined with renal insufficiency, metformin should be reduced or stopped to avoid further aggravation of liver and kidney damage. Third, lactic acidosis, metformin in the body suffering from hypoxic diseases, cardiopulmonary insufficiency is prone to lactic acidosis, should try to avoid the use. Fourth, drug allergy, a small number of patients taking metformin may appear after the skin itching, rash and other allergic conditions. Fifth, long-term use of metformin will reduce the absorption of vitamin B12, which may cause nutritional anemia.