Vitamin B12 is a water-soluble vitamin crucial for maintaining cognitive function as well as DNA and red blood cell production. Generally, adults obtain the daily recommended 2.4 mcg of vitamin B12 from consuming animal products, such as chicken, beef or fish, the Office of Dietary Supplements reports. If people are unable to consume appropriate levels of vitamin B12 from their diet or have difficulty absorbing this nutrient -- a condition called pernicious anemia -- a doctor may recommend treatment with vitamin B12 shots. Vitamin B12 shots, which may cause side effects, are a prescription injection that deliver a synthetic form of this vitamin, called cyanocoblamin, directly into the body.
Injection Site Reaction
After receiving a vitamin B12 shot, patients may develop a skin reaction at the injection site. Affected patients may notice that the injection site appears unusually swollen, red or irritated, Drugs.com warns. The treated skin region may also feel tender or painful to the touch or may begin to itch. This side effect of a vitamin B12 shot is temporary and typically subsides within a few hours of treatment. Patients should be aware that injections site reactions may recur following subsequent treatments.
Diarrhea
A vitamin B12 shot may cause diarrhea in certain patients, RxList reports. Diarrhea results in frequent bowel movement urges that yield runny, loose stools. Patients who experience diarrhea may also develop nausea, bloating, cramping or stomach pain. Diarrhea side effects are typically temporary and resolve within a few days of treatment.
Flu-like Symptoms
People may experience flu-like symptoms following treatment with a vitamin B12 shot. These flu-like side effects may include headache, fever, joint pain, weakness or dizziness, Drugs.com explains. If these side effects persist or become severe, affected patients should consult a medical professional.
Pulmonary Edema or Heart Failure
Infrequently, pulmonary edema or heart failure may occur in patients receiving treatment with vitamin B12 shots, RxList warns. Side effects of pulmonary edema or heart failure include unusual body swelling, sudden weight gain, difficulty breathing and chest pain or discomfort. Patients who experience these side effects should seek immediate medical care, as pulmonary edema and heart failure can be life-threatening without prompt treatment.
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