Metformin does not have a miraculous effect, and its effects include lowering blood glucose, reducing weight, and improving insulin resistance. Metformin through the inhibition of hepatic glucose output, increase the peripheral tissues of glucose uptake and utilization, and can improve insulin sensitivity, and then play a role in lowering blood glucose, and there is a role in weight loss, is not prone to cause hypoglycemia, commonly used in obese patients with type 2 diabetes mellitus. Metformin can also assist in the treatment of polycystic ovary syndrome. The main side effect of the drug is gastrointestinal reactions. Contraindications to metformin include type 2 diabetes combined with acute severe metabolic disorders, severe infections, hypoxia, trauma, major surgery, pregnant and lactating women. Metformin should be used under the supervision of a doctor and should not be taken on its own.