Possible side effects or “hazards” of adenosylcobalamin are allergic reactions such as skin rashes; the use of any medication has been evaluated to determine that the benefits outweigh the risks. Adenosylcobalamin is a commonly used antianemia drug for the treatment of diseases such as anemia due to vitamin B12 deficiency, and for the adjunctive treatment of diseases such as radiation-induced leukopenia. The drug has reported fewer adverse reactions, mainly due to skin rash and other symptoms caused by drug allergy. The overall safety of the drug is high, and risks are less likely to occur when the drug is administered under the supervision of a clinician. Caution is advised in the use of the drug in pregnant women, lactating women, the presence of unexplained neurological damage, allergies and other conditions. It is important to note that any medication is used for the purpose of treating or ameliorating a disease, and the clinician will assess the possible risks before the medication is administered and determine that the benefits outweigh the risks before administering the medication. Do not resist the use of medication out of fear of possible adverse effects and miss the opportunity for treatment.