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Side Effects of B12 Supplements

Vitamin B12 is the name for a group of compounds that include hydroxocobalamin and cyanocobalamin, and belong to the vitamin B Complex family. Aside from food sources, vitamin B12 may be obtained in supplements, which are available in oral or injectable form. There are a number of side effects associated with these B12 supplements.

  1. Allergic Reactions

    • People who are sensitive or allergic to cobalt and cobalamin may suffer allergic reactions to B12 supplements. An allergic reaction is commonly characterized by breathing difficulty, chest pain, and swelling of the tongue, lips and throat. This occurs because the supplements are commonly synthetic formulations of the vitamin, and contain these compounds as part of their chemical structure. If an allergic reaction occurs, the patient should seek to increase their B12 intake via dietary sources in which the vitamin occurs naturally .

    Hives

    • When a vitamin B12 injection is administered, the patient's skin may break out in a skin rash or hives (Urticaria). Hives is characterized by raised, red bumps or welts on the skin. He or she may also suffer a condition referred to as pruritus, which is characterized by an unpleasant itching sensation that triggers a reflex to scratch. Rosacea conglobata, a rare form of rosacea, has been reported to result from high doses of B12 supplements.

    Leber's Disease

    • B12 supplements can worsen the progression of a disease called Leber's Optic Atrophy. This is a hereditary disease that causes the individual's optic nerve to atrophy, eventually resulting in a loss of central vision. Ingesting vitamin B12 supplements increase the deterioration of the nerve and lead to an even more rapid loss of vision.

    Neonatal

    • Benzyl alcohol, a preservative that is contained in the vitamin B12 shot, may cause some serious side effects when given to newborn babies. The newborn may become short of breath and its heart rate may slow down. The baby's blood pressure may also drop. In some cases this preservative can even cause death. The risk of serious side effects increases if the baby had a low birth weight. The B12 injection is available in a form that does not use this preservative, and should be used for these infants.

    Additional Side Effects

    • Epocrates Online lists a number of other side effects that may result from the use of vitamin B12 supplements. Common side effects include headaches, diarrhea, nausea, ataxia, nervousness, swelling and anxiety. Serious effects listed include thrombocytosis, hypokalemia and pulmonary edema.

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