Vitamin B12 Side Effects
Generic Name: cyanocobalamin
Note: This page contains side effects data for the generic drug cyanocobalamin. It is possible that some of the dosage forms included below may not apply to the brand name Vitamin B12.
It is possible that some side effects of Vitamin B12 may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.
For the Consumer
Applies to cyanocobalamin: chewable tablets, controlled-release tablets, sublingual tablets
When used in small doses, no COMMON side effects have been reported with this product. Seek medical attention right away if any of these SEVERE side effects occur while taking cyanocobalamin (the active ingredient contained in Vitamin B12)
Severe allergic reactions (rash; hives; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue).
For Healthcare Professionals
Applies to cyanocobalamin: compounding powder, injectable solution, intramuscular solution, nasal gel, nasal spray, oral tablet, oral tablet extended release, sublingual tablet
Cardiovascular side effects associated with parenteral cyanocobalamin (the active ingredient contained in Vitamin B12) 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 (the active ingredient contained in Vitamin B12) 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 side effects associated with parenteral cyanocobalamin (the active ingredient contained in Vitamin B12) 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 (the active ingredient contained in Vitamin B12) have included arthritis, back pain, and myalgia.[Ref]
Respiratory side effects associated with parenteral cyanocobalamin (the active ingredient contained in Vitamin B12) 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 (the active ingredient contained in Vitamin B12) have included infection.[Ref]
Other side effects associated with parenteral administration of cyanocobalamin (the active ingredient contained in Vitamin B12) 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
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