In clinical practice, patients often come to inquire: "Is vitamin B12 and mecobalamin the same medicine? Can either be used?" Today, the pharmacist will explain the relationship and usage between them. Vitamin B12 is a large family of drugs, which includes four substances: cyanocobalamin, hydroxycobalamin, adenosylcobalamin, and methylcobalamin. Their difference lies in the fact that the X position connected to cobalt in the structure is a different group, which is cyano, methyl, deoxyadenosine, and hydroxyl. Our most common vitamin B12 injection or tablet is actually the cyano substituted cobalt cyanide in it. Therefore, it can be seen that although all belong to the vitamin B12 family, these four drugs are not the same drug. What are the diseases that vitamin B12 and mecobalamin can treat in clinical practice, as they are different substances that can replace each other? Upon consulting the instructions, it was found that the two are basically similar, both used for the treatment of megaloblastic anemia and neuritis. Mecobalamin is clinically effective for peripheral neuropathy such as neurological disorders and polyneuritis caused by diabetes, especially for numbness, pain and paralysis, and can be used as an auxiliary treatment for neurotrophic repair of diabetes. In the treatment of peripheral neuropathy, the clinical application of mecobalamin has better safety and efficacy. In summary, whether the two can replace each other cannot be generalized, and different situations need to be distinguished: for neurological disorders, mecobalamin should be preferred, while for megaloblastic anemia, mecobalamin and vitamin B12 have similar effects and can be replaced, but should be used reasonably under the guidance of doctors and pharmacists. This type of special population should be cautious when using mecobalamin. Mecobalamin is a commonly used drug for peripheral neuropathy. For special populations such as pregnancy and lactation, there is relatively little research data on mecobalamin, and its safety is not clear. Methylcobalamin is the main active form of vitamin B12 in the body, but it is essentially two drugs compared to vitamin B12. Special populations during pregnancy or lactation should use it under the guidance of a physician or pharmacist, and should not only consider it as a vitamin preparation, ignoring its potential hazards and causing adverse effects on pregnancy or lactation. Wen/Ma Xiaowei (Beijing Shijitan Hospital) (Liaoxin News Agency)