Metformin remains the first-line medication for treating type 2 diabetes. The primary side effects of metformin are gastrointestinal in nature. Patients may experience dry mouth, bitter taste, bad breath, or a metallic taste in the mouth. Some patients may experience decreased appetite or even anorexia, while others may experience nausea, vomiting, or diarrhea. When these adverse reactions are particularly severe, it may be advisable to reduce the dosage of metformin. Once the patient's adverse reactions gradually improve and they can tolerate metformin treatment, the dosage can be adjusted again to achieve the goal of good blood sugar control. Less common adverse reactions to metformin may include allergic reactions. Additionally, when patients have concurrent respiratory insufficiency, the body is in a state of relative ischemia and hypoxia, and the use of metformin may trigger lactic acidosis. Metformin is primarily metabolized and excreted through the kidneys and liver, and it does not have a direct damaging effect on these organs.