Metformin should not be taken in pregnancy. Contraindications to metformin include type 2 diabetes mellitus combined with acute severe metabolic disorders, severe infections, hypoxia, trauma, major surgery, pregnant and lactating women. Metformin is used as a first-line agent in the treatment of type 2 diabetes, either alone or in combination with other drugs. When used in patients with type 1 diabetes, combination with insulin may reduce insulin dosage and blood sugar fluctuations. The main side effect of metformin is gastrointestinal reaction, by taking the drug with meals, starting from a small dose and gradually increasing the dose, it can reduce gastrointestinal adverse reactions, some patients may also have other adverse reactions, and there is individual variability in adverse reactions. The use of drugs during pregnancy need to consult a professional doctor, avoid blind use of drugs, so as to avoid adverse effects on the mother or fetus.