Metformin belongs to the class of biguanide hypoglycemic drugs, the main pharmacological effect of metformin is to reduce blood glucose by inhibiting hepatic glucose output, improving the sensitivity of peripheral tissues to insulin, increasing the uptake and utilization of glucose. Metformin is often used as a first-line drug 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 glucose fluctuations. Contraindications of metformin include type 2 diabetes mellitus combined with acute severe metabolic disorders, severe infections, hypoxia, trauma, major surgery, pregnant and lactating women, etc.; those who are allergic to the drug or have serious adverse reactions; alcoholics and so on. Metformin should be consulted with a medical professional before use.