Metformin is the first-line drug of choice recommended by diabetes guidelines. It has the ability to increase the body’s insulin sensitivity, reduce hepatic glucose output and decrease intestinal absorption of sugar. Metformin alone is effective in reducing fasting and postprandial glucose and also has a significant improvement in glycated hemoglobin, which can be reduced by 1.5%-2%. Metformin reduces cardiovascular events and mortality due to overweight and obesity and needs to be administered throughout the course of treatment when there are no contraindications. Metformin also reduces LDL-cholesterol and triglyceride levels. The efficacy of metformin is closely related to the dose and is best at 1500-2000 mg/d. Metformin does not cause hypoglycemia or weight gain, but it is also important to look at the adverse effects of metformin and its precautions. Some patients with hyperglycemia may experience gastrointestinal discomfort after taking metformin orally, such as nausea, vomiting, indigestion, bloating, abdominal pain, constipation; in some cases, abnormal taste, such as metallic taste, muscle pain, palpitations, flushing, rash, weakness, flu-like symptoms, and other adverse reactions. In the case of gastrointestinal reactions, different dosage forms can be selected appropriately, or consider taking the drug after meals, followed by oral ranitidine, etc.