The use of methylcobalamin does not usually cause fever, but fever cannot be ruled out in people with specific allergies. Methylcobalamin belongs to the endogenous coenzyme B₁₂, which can help promote the synthesis of proteins and nucleic acids, promote the synthesis of myelin sheaths, and is also beneficial in restoring the delay in the communication of nerve bonds. The primary routes of administration for methylcobalamin are oral and intravenous, and it is primarily used in the treatment of peripheral neuropathies and macrocytic anemia due to vitamin B₁₂ deficiency. The relatively common adverse reactions are nausea, vomiting, and loss of appetite, and there are no fever-related adverse reactions. If fever occurs while taking methylcobalamin, you should go to the hospital as soon as possible to clarify the exact cause of the fever so as not to delay the diagnosis and treatment.