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Cyanocobalamin Side Effects

For the Consumer

Applies to cyanocobalamin: intramuscular solution

Other dosage forms:

In addition to its needed effects, some unwanted effects may be caused by cyanocobalamin. In the event that any of these side effects do occur, they may require medical attention.

If any of the following side effects occur while taking cyanocobalamin, check with your doctor or nurse immediately:

Incidence not known:
  • Abdominal or stomach pain
  • bleeding from the gums or nose
  • blue lips and fingernails
  • chest pain
  • cough
  • coughing that sometimes produces a pink frothy sputum
  • decreased urine output
  • difficult, fast, noisy breathing, sometimes with wheezing
  • difficulty with swallowing
  • dilated neck veins
  • dizziness
  • extreme fatigue
  • eye pain
  • fast heartbeat
  • headache
  • hives, itching, or skin rash
  • increased sweating
  • irregular breathing
  • irregular heartbeat
  • pale skin
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • ringing in the ears
  • swelling of the face, fingers, feet, or lower legs
  • tightness in the chest
  • unusual tiredness or weakness
  • weight gain

Minor Side Effects

Some of the side effects that can occur with cyanocobalamin may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

Incidence not known:
  • Diarrhea
  • skin rash with a general disease

For Healthcare Professionals

Applies to cyanocobalamin: compounding powder, injectable solution, intramuscular solution, nasal gel, nasal spray, oral tablet, oral tablet extended release, sublingual lozenge, sublingual tablet


Cardiovascular side effects associated with parenteral cyanocobalamin have included congestive heart failure, pulmonary edema, and peripheral vascular thrombosis. These effects were usually reported early in treatment.[Ref]


Dermatologic side effects associated with both intranasal and parenteral cyanocobalamin have included itching and transitory exanthema.

Dermatologic side effects have rarely included exacerbation or onset of inflammatory acne and folliculitis related to B12.[Ref]

Exacerbation or onset of inflammatory acne and folliculitis have been seen with high doses of B12 (5 to 10 mg/week). The etiology and pathogenic mechanisms of vitamin B12-induced acne are unknown. When present, acneiform eruptions usually occur on the facial area after the first or second injection, and typically disappear within 8 to 10 days after stopping therapy.

A single case of a severe skin eruption resembling acne rosacea that was temporally associated with daily ingestion of 100 mcg of B12 (with 100 mg of B6) has been reported. The rash resolved upon discontinuation of both drugs and recurred upon rechallenge with half the doses.

Some have suspected sorbitol or iodine that is present in some ampules of B12 may be the cause of at least some cases of skin eruptions associated with this drug.[Ref]


A single case of cecal vitamin B12 bezoar has been reported in an elderly man with a history of multiple gastrointestinal surgeries.[Ref]

Gastrointestinal side effects associated with parenteral cyanocobalamin have included dyspepsia, nausea, vomiting, and mild transient diarrhea.

Gastrointestinal side effects associated with intranasal cyanocobalamin have included glossitis and nausea.[Ref]


Anaphylactic reactions have been reported primarily with parenteral administration of B12 and are thought to be the result of impurities of B12 preparations that are no longer manufactured. They may occur soon after a sensitizing dose, within a few weeks or months, or rarely after a latency of several years.[Ref]

Hypersensitivity side effects associated with parenteral cyanocobalamin have rarely included anaphylactic reactions and death.[Ref]

Nervous system

Nervous system side effects associated with parenteral cyanocobalamin have included abnormal gait, asthenia, anxiety, dizziness, hypoesthesia, incoordination, nervousness, and incoordination.

Nervous system side effects associated with both parenteral and intranasal cyanocobalamin have included paresthesia and headache.[Ref]


Hematologic side effects have included polycythemia vera.[Ref]


Musculoskeletal side effects associated with parenteral cyanocobalamin have included arthritis, back pain, and myalgia.[Ref]


Respiratory side effects associated with parenteral cyanocobalamin have included dyspnea.

Respiratory side effects associated with both parenteral and intranasal cyanocobalamin have included rhinitis.[Ref]


Immunologic side effects associated with both parenteral and intranasal cyanocobalamin have included infection.[Ref]


Other side effects associated with parenteral administration of cyanocobalamin have included feeling of swelling of entire body, back pain, and generalized pain.[Ref]


1. "Product Information. Nascobol (cyanocobalamin nasal)." Schwarz Pharma, Mequon, WI.

2. Sherertz EF "Acneiform eruption due to "megadose" vitamins B6 and B12." Cutis 48 (1991): 119-20

3. Gallastegui C, Cardona D, Pujol R, Garcia B, Bonal J, Andreu A "Vitamin B12-induced folliculitis." DICP 23 (1989): 1033-4

4. Dupre A, Albarel N, Bonafe JL, Christol B, Lassere J "Vitamin B-12 induced acnes." Cutis 24 (1979): 210-1

5. Malten KE "Flare reaction due to vitamin B12 in a patient with psoriasis and contact eczema." Contact Dermatitis 1 (1975): 325-6

6. Hunt-Fugate AK, Schmidt HJ "Cecal vitamin bezoar formation inducing abdominal discomfort." Ann Pharmacother 26 (1992): 485-7

7. Hovding G "Anaphylactic reaction after injection of vitamin B12." Br Med J 3 (1968): 102

8. Ugwu CN, Gibbins FJ "Anaphylactic reaction to vitamin B12 appearing after several years of therapy." Age Ageing 10 (1981): 196-7

9. Sawyer DR "Cyanocobalamin and cyanide toxicity." Am Fam Physician 26 (1982): 48

Not all side effects for cyanocobalamin may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

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