What Are the Side Effects of Vitamin B12 Shots?

By Staff WriterLast Updated Mar 28, 2020 1:10:19 PM ET
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The main side effects of a vitamin B12 injection include redness at the injection site, mild diarrhea, itching or a feeling of swelling all over the body, according to MedicineNet. If these side effects persist or get worse, contact the doctor or pharmacist immediately. An injection of vitamin B12 may cause low potassium levels in the blood, a condition known as hypokalemia.