Based on the data of foreign and domestic literature, the question of the possible carcinogenesis of vitamin B₁₂ and the expediency of its administration to patients with cancer who have neurological complications due to chemotherapy is analyzed. The absence of convincing direct evidence of the carcinogenic effect of cyanocobalamin has been demonstrated, as well as the reasonableness of drug correction of vitamin B₁₂ deficiency in cancer patients in order to prevent the development of characteristic deficient neurological disorders. The question of the effectiveness of oral administration of cyanocobalamin at a dose of 1 mg per day is considered.