Methylcobalamin and vitamin B12 cannot be used together because they are repeated medications.1. Methylcobalamin is an endogenous vitamin B12 and widely exists in human blood and spinal cord as coenzyme B12, which is mainly used clinically for nerve nutrition to promote the recovery of myelin sheath of various nerves, and the therapeutic effect of methylcobalamin is better than vitamin B12.2. Vitamin B12 also has the function of treating anemia and is a raw material for hematopoiesis. Clinical methylcobalamin is expensive while vitamin B12 is relatively cheap, but the efficacy of both is similar, so clinical methylcobalamin and vitamin B12 cannot be applied at the same time.