Metformin: This diabetes medication might impair vitamin B12 absorption in some people
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Report side effects with Vitamin B12 To your doctor
What are B12 injections, and how do they work
Most medical documents indicate you might experience any of these: Mild diarrhea and/or upset stomach Difficulty breathing or swallowing Weight loss or weight gain Nervousness or restlessness Nausea or vomiting Headaches or migraines Paresthesias (tingling sensations) Rhinitis (chronic sneezing or a congested, drippy nose) Skin reactions, such as rash, itching, swelling, blisters, or pain at the site of injection Light joint pain Lightheadedness or dizziness Chest pain or discomfort Low blood potassium levels Irregular heartbeat Chills, night sweats, fever, or hot flushes General feeling of sickness However, people often fail to recognize that many side effects of vitamin B12 injections are consistent with B12 deficiency itself