Methylcobalamin is a derivative of vitamin B12, which has nutritional and restorative effects on nerve cells, and there is no authoritative data on the fastest effective time, generally about 1 week of clinical use of the drug can be effective, but the specific effective time varies from person to person. Mecobalamin is mainly used for megaloblastic anemia and peripheral neuropathy caused by vitamin B12 deficiency. The clinical efficacy of this drug can generally be observed in about 1 week of use, the course of treatment is generally 1 month, if the drug is ineffective for 1 month, then adjust the medication as prescribed by the doctor. Adverse reactions after the use of this product include loss of appetite, nausea, vomiting, diarrhea, skin rash, etc. It is contraindicated for patients who are allergic to this product. It is recommended to adhere to the medication under the guidance of a doctor and regularly review the condition.