Metformin is available in different dosage forms, such as metformin tablets, which are recommended to be taken after meals; metformin enteric tablets, which are recommended to be taken 20-30 minutes before meals; and metformin extended-release tablets, which are taken once a day and recommended to be taken at night. Metformin is a classical hypoglycemic drug, which works through muscle and liver, and the main side effect is irritation of gastrointestinal tract. Conventional hypoglycemic drugs should be taken immediately after meals, and patients with gastric disease and gastric ulcer should take it during meals to reduce gastric irritation. Therefore, metformin tablets are mostly chosen to be taken after meals, which is safer and has less side effects. Enterosoluble metformin has no gastrointestinal reaction, and can be chosen to take 20-30 minutes before meal, 2-3 times a day, the dose needs to be determined according to the high or low blood sugar. In case of metformin extended-release tablets, it is not necessary to take it in synchronization with diet, but it is usually recommended to take it at night. Glucose-lowering drugs need to be used strictly according to the method of the drug instructions. Different dosage forms of metformin have different requirements for the best time to be taken, and the specific dosage and usage should be taken according to medical advice.