Vitamin B12 injections (cobalamin or cyanocobalamin) are usually prescribed by physicians for patients that are suffering from a vitamin B12 deficiency or from anemia or fatigue. Vitamin B12 is important for helping make red blood cells.
Possible Painful Injection
Because vitamin B12 injections are intramuscular injections that must be made deep under the skin, they can be quite painful.
Less Serious Side Effects
Although not a complete list, you may experience dizziness, headache, weakness, upset stomach, nausea, diarrhea, fever, joint pain, itching, rash, numbness, tingling or irritation, or pain at the injection site.
Serious Side Effects
Seek immediate medical attention if any serious allergic reactions that include difficulty breathing, swelling of the lips, tongue, face or throat or hives occur. Chest pain, shortness of breath, rapid weight gain, swelling and redness, warmth or pain in the leg are also considered to be serious side effects for which you should call your doctor right away.
Vitamin B12 shots are usually given every day or every other day for a couple of weeks in order to treat a vitamin B12 deficiency. Maintenance injections are given between one to three months as determined by the physician.
If you have Leber's disease (a disease that causes poor vision and sometimes blindness) or are allergic to cobalt, you should not take vitamin B12 injections. Those with Leber's disease could have optic nerve damage possibly leading to blindness if they are injected with vitamin B12.