Metformin is a very commonly used glucose-lowering medication, and there are a number of side effects that may occur with long-term use of metformin. The most common side effects typically seen during initial treatment include causing nausea, vomiting, diarrhea, abdominal pain, and loss of appetite. Most patients are usually relieved on their own and there is nothing to worry about. Gastrointestinal tolerance can be improved by slowly increasing the dosage of metformin, and if patients are really intolerant they can see their doctor to change to another hypoglycemic agent. Another very rare side effect of metformin is lactic acidosis, which needs to be taken care of. Long-term use of metformin may reduce the absorption of vitamin B12, and if a patient develops megaloblastic anemia, it should be considered to be related to metformin. When taking metformin, there may also be taste disorders, including the possibility of liver function test abnormalities of these side effects, in the use of the drug must pay attention to observation, there are abnormalities in time to consult the doctor.