Metformin belongs to the class of biguanide glucose-lowering drugs and is generally used clinically for the treatment of type 2 diabetes mellitus in which exercise therapy is ineffective and dietary control alone is ineffective. This drug is contraindicated in people with metformin allergy, heart failure, severe infection and trauma, and diabetic ketoacidosis. Its common side effects include gastrointestinal reactions, anemia, etc. A small number of people taking it may experience other side effects. 1. Gastrointestinal reaction: People taking the drug may experience gastrointestinal reactions such as nausea, diarrhea, flatulence, vomiting, dyspepsia, and fatigue, which are usually short-lived and mild. 2. Anemia: this drug will reduce the intestinal absorption of vitamin B12, resulting in a decrease in hemoglobin, leading to macrocytic anemia. 3. Others: The patient may also experience stool abnormalities, dizziness, myalgia, hypoglycemia, lightheadedness, skin rash, nail abnormalities, abnormal taste, increased sweating, chest discomfort, etc., which are generally rare. In severe cases, lactic acidosis may occur. Metformin needs to be taken in accordance with the doctor’s instructions, and should not be used arbitrarily, so as not to lead to serious consequences, and during the period of taking the drug, you need to monitor the changes in blood glucose, and check the renal function on a regular basis. If you feel unwell, please consult a doctor promptly.