Vitamin B12 is involved in the metabolism of folic acid, and its deficiency causes impaired nucleic acid synthesis. Vitamin B12 is mainly used in megaloblastic anemia and as an adjunct to subacute combined degenerative neurological lesions such as neuritis. Vitamin B12 is involved in the metabolism of several important substances in the body, such as the cycle of tetrahydrofolate. Its deficiency causes megaloblastic anemia, as well as affects the synthesis of fatty acids, and symptoms of neurological damage can occur. The main adverse reaction to vitamin B12 preparations is allergic reaction, but the incidence is low. Occasionally, it can be seen to cause rash, itching, diarrhea and allergic asthma, and rarely anaphylaxis. It is contraindicated in persons with known hypersensitivity to vitamin B12, or in persons who have previously experienced allergic symptoms (e.g., eye congestion, itching, swelling, rash) due to ophthalmic medications. Use with caution in patients with glaucoma. This drug is a prescription drug, and must be used under the guidance of a doctor to regulate the use of medication, not blindly on their own, in order to avoid delays in the condition.