Metformin is an oral hypoglycemic drug commonly used by diabetic patients, the side effects of long-term use of metformin are as follows: First, gastrointestinal reactions, long-term use of metformin can occur nausea, vomiting, diarrhea, metallic taste in the mouth and other gastrointestinal symptoms, it is recommended to take after meals to reduce the stimulation of the gastrointestinal tract. Second, long-term use of metformin has the risk of triggering lactic acidosis in patients with cardiopulmonary insufficiency or hypoxic diseases. Long-term use of metformin may cause liver damage, so metformin is contraindicated in patients with hepatic insufficiency. Fourth, a small number of patients may have metformin allergy, such as rash, itchy skin, etc. Fifth, metformin has a weight-lowering effect on obese patients, and a few patients who consume metformin for a long time may lead to weight loss or even wasting.