Last updated on RxList: 11/3/2020
Cyanocobalamin Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

What Is Cyanocobalamin?

Cyanocobalamin (vitamin B12) is a man-made form of vitamin B12 used to treat low levels (deficiency) of Vitamin B12. A B12 deficiency may occur in certain health conditions (e.g., poor nutrition, stomach/intestinal problems, infection, cancer) and may result in anemia, stomach problems, and nerve damage. Cyanocobalamin is available in generic form.

What Are Side Effects of Cyanocobalamin?

Common side effects of Cyanocobalamin include:

  • injection site reactions (pain, redness, swelling, irritation),
  • diarrhea,
  • nausea,
  • upset stomach,
  • itching,
  • rash,
  • headache,
  • dizziness,
  • weakness,
  • numbness or tingling,
  • fever,
  • joint pain, or
  • a feeling of swelling all over the body.

Cyanocobalamin may cause low potassium levels in the blood (hypokalemia). Tell your doctor if you have unlikely but serious side effects of Cyanocobalamin including:

Dosage for Cyanocobalamin

To treat pernicious anemia a dose of 100 mcg daily of Cyanocobalamin for 6 or 7 days should be administered by intramuscular or deep subcutaneous injection.

What Drugs, Substances, or Supplements Interact with Cyanocobalamin?

Cyanocobalamin may interact with drugs that may affect blood cell production (e.g., chloramphenicol, anti-cancer drugs, HIV drugs), or supplements such as folic acid. Tell your doctor all medications and supplements you use.

Cyanocobalamin During Pregnancy and Breastfeeding

During pregnancy, Cyanocobalamin should be used only when prescribed. This medication may pass into breast milk. Consult your doctor before breastfeeding.

Additional Information

Our Cyanocobalamin (vitamin B12) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


According to the USDA, there is no difference between a “portion” and a “serving.” See Answer
Cyanocobalamin Consumer Information

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Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • heart problems--swelling, rapid weight gain, feeling short of breath;
  • fluid build-up in or around the lungs--pain when you breathe, feeling short of breath while lying down, wheezing, gasping for breath, cough with foamy mucus, cold and clammy skin, anxiety, rapid heartbeats; or
  • low potassium level--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Common side effects may include:

  • diarrhea; or
  • swelling anywhere in your body.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Cyanocobalamin (Cyanocobalamin)


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Cyanocobalamin Professional Information



Anaphylactic shock and death have been reported with administration of parenteral vitamin B12 (see WARNINGS).


Pulmonary edema and congestive heart failure early in treatment; peripheral vascular thrombosis.


Polycythemia vera


Mild transient diarrhea


Itching; transitory exanthema


Feeling of swelling of entire body

Read the entire FDA prescribing information for Cyanocobalamin (Cyanocobalamin)

© Cyanocobalamin Patient Information is supplied by Cerner Multum, Inc. and Cyanocobalamin Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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