Metformin is usually effective in 3 to 5 days, and it is recommended to follow a course of medication as prescribed by your doctor. Metformin is a glucose-lowering drug for patients with type 2 diabetes who are not satisfied with dietary control alone. Generally, after 3~5 days, the blood concentration in the body is gradually stabilized, and the effect of lowering sugar will appear. The absorption and utilization of the drug is different for different patients, so the exact time of seeing the effect will also be different. Metformin may have adverse reactions such as nausea, vomiting, diarrhea, abdominal pain, abnormal taste, etc. It is contraindicated in patients with renal disease, heart failure, acute myocardial infarction and metabolic acidosis. The medication should be used under the guidance of a doctor, read the drug instructions carefully before use, do not blindly use the drug on your own.