b12 injection safe Safety, Side Effects & Risks Vitamin B12 Injections: What You

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Side effects from B12 supplementation are uncommon but may include: Mild gastrointestinal symptoms such as nausea or diarrhoea, typically with very high oral doses Headache or dizziness in some individuals Skin reactions (rash, itching) at injection sites when using intramuscular preparations Rare but serious allergic reactions, including anaphylaxis with injectable forms Hypokalaemia (low potassium) may occur during rapid correction of severe megaloblastic anaemia If you experience symptoms of a severe allergic reaction (difficulty breathing, severe rash, swelling of face or throat) after taking B12, seek immediate medical attention

Mast Cell Activation Syndrome. Cleveland Clinic, Accessed 14 May 2026