Methylcobalamin is used to nourish the nerves, promote the synthesis and metabolism of nutrients in brain cells, and improve neuronal conduction, and should be used in accordance with the doctor’s instructions. Mecobalamin is commonly used as tablets, capsules, dispersible tablets and injections, which belongs to endogenous coenzyme B12, and is mostly used in the treatment of megaloblastic anemia caused by vitamin B12 deficiency and peripheral neuropathy. It should be noted that people with a history of allergy to methylcobalamin or any of the excipients in the prescription are prohibited from using any preparation of this drug. Some patients may experience allergic reactions, such as loss of appetite, nausea, vomiting, diarrhea, herpes, etc., and should consult a doctor promptly if the symptoms are more serious. Patients should follow the doctor’s instructions to use any preparation of methylcobalamin, avoid blindly using the drug, in order to avoid allergic reactions, or affect the condition.