Long-term administration is generally without side effects, but a few patients may have side effects, including diarrhea, vomiting, and skin rash. Methylcobalamin, i.e. endogenous vitamin B12, long-term use may lead to gastrointestinal reactions, such as diarrhea, bloating, loss of appetite, acid reflux, nausea, vomiting, etc., and a few patients may have skin rashes, fever, easy sweating, and hard knots and pain at the site of intramuscular injection, and those with severe allergic reactions may have a drop in blood pressure and respiratory distress. Methylcobalamin is easy to enter the neuronal organelles, has obvious regulatory effect on the nervous system, can participate in brain cells and spinal cord neurons, thymine nucleoside synthesis, promote the utilization of folic acid and nucleic acid metabolism, with the role of promoting nucleic acid and protein synthesis. Clinically, it is mainly used in the treatment of various nerve injuries, neuritis, neuralgia, peripheral neuropathy, and promotes the role of nerve function recovery. The medication should be taken in accordance with the doctor’s instructions and standardized to avoid unauthorized use of medication.