Metformin is a commonly used oral drug for the treatment of diabetes mellitus, the main adverse reactions are nausea, vomiting, abdominal distension, diarrhea and other symptoms, while lactic acidosis, a very rare but serious adverse reaction, can be manifested as acidosis dyspnea, abdominal pain, muscle cramps, etc., which can lead to death if it is not treated in time. When metformin accumulates in the body, it may cause lactic acid-induced poisoning. There will be nausea, vomiting, abdominal pain and other gastrointestinal symptoms; purple lips, deep and large breathing, or even dyspnea; accelerated heart rate, blood pressure drop and other manifestations; muscle convulsions, impaired consciousness, or even death. Once lactic acidosis occurs, it is recommended to seek immediate medical treatment. Metformin is contraindicated in any metabolic acidosis, hepatic or renal insufficiency, dehydration, severe infection, shock, etc. Patients using Metformin are advised to take the drug as prescribed by the doctor to avoid adverse consequences. Patients who have already experienced the above symptoms need to go to the hospital in time, under the guidance of the doctor for targeted treatment.