B12 Side Effects

Possible side effects of B12 are listed below. Call your doctor if these side effects are severe or do not go away in a few days.

• Diarrhea.
• Headache.
• Weakness.
• Sensation that the entire body is swollen.

Some of the adverse effects of vitamin B12 are more serious. Call your doctor without delay or seek emergency medical attention if you develop the following signs and symptoms:

• An unusual or allergic reaction with hives, skin rash, itching.
• Difficulty breathing or swallowing.
• Coughing or wheezing.
• Swelling of the arms, legs, hands, or feet.
• Extreme thirst.
• Frequent urination.
• Confusion.
• Shortness of breath, especially with exercise or lying down.
• Muscle weakness, cramps, or pain.
• Extreme tiredness.
• Fast heartbeat.
• Pain, redness, or swelling in one leg.

The above list may not include all the potential side effects of B12. Tell your doctor if the side effects are severe or last more than a few days. You can also report unusual side effects to the Food and Drug Administration at 1-800-FDA-1088.

B12 Overdose: In case of an overdose of B12, call your doctor immediately or seek emergency medical help. You can also call the local poison control center or national poison control center at 1-800-222-1222. If a person has difficulty breathing, cannot be awakened, or has had a seizure, call 911.

Source: FDA