Warnings

Cyanocobalamin (Vitamin B-12)

Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Jul 08, 2025

Warnings

Cyanocobalamin Risks, Warnings, and Complications

Cyanocobalamin may cause or worsen health problems in some people. Talk to your doctor or pharmacist before taking any vitamin supplementation. Some of the risks of taking cyanocobalamin include:

DRUG INTERACTIONS: Certain medications can cause changes in the gut so that you can’t properly absorb vitamin B-12. Talk to your doctor about checking your vitamin B-12 status if you take gastric acid reducers or the diabetes medication metformin.
OVERDOSE: Do not exceed the recommended dose of cyanocobalamin. Talk to your doctor before taking vitamin B-12 supplementation if you have vascular disease (blood vessel problems), heart disease, a history of stroke, diabetes, bleeding disorders, or blood clotting problems, are pregnant or nursing, or are scheduled for surgery soon.
CONTRAINDICATIONS: People with the following medical conditions should not receive vitamin B-12 injections or should receive them with caution:

Leber’s disease (hereditary optic nerve atrophy) - treatment with vitamin B-12 supplement can result in a serious medical problem (severe and rapid optic atrophy).
Intense treatment of megaloblastic anemia (this can result in hypokalemia (low blood potassium levels) and death).
Anaphylactic shock (a very serious allergic reaction) - your doctor may do an intradermal test before giving you vitamin B-12 by injection.
Gasping syndrome in premature infants due to the presence of benzyl alcohol in the injection product.
Aluminum toxicity in patients with kidney disease and premature newborn babies.

Precautions Before Starting Cyanocobalamin

Tell your doctor if you have ever had an allergic reaction to cyanocobalamin, any of the active or inactive ingredients in cyanocobalamin formulations, hydroxocobalamin, cobalt, multivitamins, or any other medications. Your pharmacy can give you a list of ingredients.

Give your doctor and pharmacist a complete list of your medications, including prescription medications, over-the-counter medicines, vitamins, dietary supplements, and herbal products. This can help avoid possible drug interactions between cyanocobalamin and your other medicines.

Cyanocobalamin may not be safe for people with certain health conditions. Give your doctor a complete medical history before starting any dietary supplements. Tell your doctor if you have Leber’s hereditary optic neuropathy, kidney disease, or a history of excessive alcohol consumption.

Tell your doctor if you are pregnant, could be pregnant, plan to get pregnant soon, or nursing an infant with breast milk.

Precautions During Use of Cyanocobalamin

Keep all your medical and lab appointments. Your doctor may want to order certain lab tests, such as a complete blood count (CBC), to check your response to cyanocobalamin supplementation.

Take cyanocobalamin regularly to get the most benefit. If you stop treatment, you may develop anemia again, and your symptoms may come back. Low vitamin B-12 levels are associated with nervous system involvement (nerve damage).

Tell lab personnel you are on cyanocobalamin. This supplement can result in false test results for certain lab tests.

Tell your doctor if you become pregnant while on this medication.

Cyanocobalamin Drug Interactions

Other drugs can affect how cyanocobalamin works. Possible interactions with certain medications can increase the risk of severe adverse effects.

Give your doctor or pharmacist a complete list of your medications, including prescription drugs, nonprescription drugs, dietary supplements, and herbal products. Also, tell your healthcare professional if you smoke, drink alcohol, or use recreational drugs because some of these substances can cause serious health complications when used with prescription medications, over-the-counter medicines, and dietary supplements.

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