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B12 Injections Side Effects

author image Jacques Courseault
As a physical medicine and rehabilitation physician I have extensive experience in musculoskeletal/neurological medicine that will benefit the network.
B12 Injections Side Effects
Vitamin B12 injection Photo Credit NikiLitov/iStock/Getty Images


Vitamin B12 (cyanocobalamin) is a synthetic form of vitamin B12. According to Drugs.com, vitamin B12 is important for growth, cell reproduction, blood formation, and protein and tissue synthesis. This essential vitamin is found in fish, shellfish, meat and dairy products. Vitamin B12 deficiency is rare because the body stores several years' worth of vitamin B12, but it can occur in people with pernicious anemia or other medical conditions. The Mayo Clinic reports that vitamin B12 injections are effective in treating dietary vitamin B12 deficiency. As with all medications, you should be aware of the possible side effects of vitamin B12 injections before receiving them.

Serious Side Effects

Serious side effects can occur when taking vitamin B12, including chest pain, shortness of breath, swelling, unusual warmth, and redness or pain in an arm or leg. These side effects may occur because your dosage is too high, or your body is sensitive to the effects of vitamin B12. Always call 911 and seek emergency medical treatment if you are experiencing these serious side effects, especially chest pain or shortness of breath.

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Less Serious Side Effects

According to Drugs.com, less serious side effects include headache, dizziness, weakness, nausea, upset stomach, diarrhea, numbness, tingling, pain or irritation at the injection point, fever, joint pain, itching or rash. These effects may improve as your body adapts to repeated injections. Always tell your doctor of unusual or irregular effects from the injections.

Effect on Heart Stents

The Mayo Clinic reports that patients undergoing heart stent placement should not take vitamin B12 injections with folic acid and vitamin B6. This combination of vitamins can increase the rate in which the heart stent can become blocked. Therefore, alert your doctor if you are taking any of these additional supplements.

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