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Last reviewed on RxList: 12/12/2016
Cyanocobalamin Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 11/11/2016

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. 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:

  • muscle cramps, or
  • irregular heartbeat.

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

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.

Cyanocobalamin Consumer Information

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

Call your doctor at once if you have a serious side effect such as:

  • chest pain;
  • feeling short of breath, even with mild exertion;
  • swelling, rapid weight gain; or
  • unusual warmth, redness, or pain in an arm or leg.

Less serious side effects may include:

  • headache, dizziness, weakness;
  • nausea, upset stomach, diarrhea;
  • numbness or tingling;
  • pain, swelling, redness, or irritation where the injection was given;
  • fever;
  • joint pain; or
  • itching or rash.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Cyanocobalamin (Cyanocobalamin)

Cyanocobalamin Professional Information


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

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

Hematological: Polycythemia vera

Gastrointestinal: Mild transient diarrhea

Dermatological: Itching; transitory exanthema

Miscellaneous: Feeling of swelling of entire body

Read the entire FDA prescribing information for Cyanocobalamin (Cyanocobalamin)

Related Resources for Cyanocobalamin

Read the Cyanocobalamin User Reviews »

© 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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