What are the side effects for cyanocobalamin (Vitamin B12)?

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Some common side effects for cyanocobalamin (Vitamin B12) include diarrhea or a feeling that your body is swollen. But other side effects can be much more severe. If you or someone you know has any of the following rare side effects, call the doctor right away:

  • Confusion
  • Coughing or wheezing
  • Difficulty breathing or swallowing
  • Dizziness
  • Extreme thirst or tiredness
  • Fast heartbeat
  • Frequent urination
  • Headaches
  • Hives, itching or rash
  • Leg pain
  • Muscle weakness, cramps or pain
  • Pain, warmth, redness, swelling or tenderness in one leg
  • Red skin color, especially on the face
  • Shortness of breath when exercising or lying down
  • Swelling of the arms or legs
  • Unusual bleeding or bruisin