Vitamin B12 is mainly used in the treatment of pernicious anemia, and in combination with folic acid for the treatment of megaloblastic anemia, it must be injected intramuscularly or intravenously, and needs to be used for a lifetime, and is not effective when taken orally, so be aware of the adverse effects, such as allergic rashes, diarrhea, and so on. It can also be used for neurological disorders, such as neuritis, neural atrophy, and so on. Elderly patients eating vitamin B12 is beneficial, can improve the memory ability of the elderly, improve memory and reduce brain atrophy, for the prevention of Alzheimer’s disease has a supporting role, so the elderly will be used as a health care drug for long-term use or intravenous use, effective for some patients, and in the process of using the drug to pay attention to adverse reactions.