What side effects does cyanocobalamin cause?

Possible side effects of cyanocobalamin (also known as vitamin B12) may include diarrhea or mild skin itching. In rare cases, cyanocobalamin may cause allergic reactions, with symptoms including hives, trouble breathing and/or swelling of the face, hands, mouth and throat. Call your doctor at the first sign of these symptoms. Do not take cyanocobalamin supplements or any dietary supplement without consulting your doctor first.
Based on information from iGuard.org, a free medication monitoring service, 5% of patients experience side effects while taking Cyanocobalamin. Some of the side effects reported by iGuard members include: Muscle Pain/Cramps, Drowsiness, Grogginess/Confusion, and Fatigue. Please follow up with your doctor or other healthcare provider if you are experiencing any symptoms that worsen or do not go away.