B12 Active

( Cyanocobalamin Injection )

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

Last Reviewed: Feb 01, 2023

Warnings

B12 Risks, Warnings, and Complications

Taking B12 can lead to serious adverse effects in some people. Some of the risks of B12 injections include:

OPTIC NERVE DAMAGE: People who have a rare eye condition called Leber's hereditary optic neuropathy can develop severe eye damage, possibly blindness, if they take B12. Always check with your healthcare professional before starting any supplement, including B12.
LOW POTASSIUM LEVELS: High doses of B12 can lead to low potassium levels in the blood, which can cause life-threatening heart rhythm abnormalities. Your health care provider may order frequent medical tests during B12 treatment to keep an eye on potassium levels.
HIGH PLATELET COUNT: Taking high-dose B12 can lead to abnormally high platelet counts in the blood, which can lead to excessive blood clotting. Keep all your appointments for laboratory tests to monitor for this side effect.
FOLATE DEFICIENCY ANEMIA: Anemia can occur for various reasons, including low B12 and low folic acid levels. Taking B 12 can make it harder to identify folic acid deficiency. Your doctor will order tests to find out what is causing your anemia and treat it accordingly.
POLYCYTHEMIA VERA: Polycythemia vera is a rare type of bone marrow cancer in which there is a high number of red blood cells. Low B12 levels can mask the symptoms of this condition. Taking B12 can help identify this condition. Tell your doctor if you experience symptoms such as numbness and tingling, fullness in the left abdomen, or itching after warm showers or baths while taking B12.
ALLERGIC REACTION: In a small number of people, B12 injections can cause severe allergic reactions. Your healthcare professional will check for this by injecting a small amount of B12 before giving you a full dose.
RISKS ASSOCIATED WITH INJECTABLE B12: The injectable form of B12 contains a preservative called benzyl alcohol, which can be very dangerous for premature babies. Injectable B12 also contains aluminum which can cause problems in premature babies and people with kidney disease. Talk to your health care professional about the risks versus benefits of injectable B12.

Precautions Before Starting B12

Tell your healthcare provider if you have ever had an allergic reaction to B12 injections, oral formulations, or nasal spray, hydroxocobalamin, other vitamins, or any other medicines. Your pharmacy can give you a list of active and inactive ingredients in B12 injections.

Give your doctor and pharmacist a complete list of your medications, including prescription and nonprescription medications, vitamins, supplements, and herbal products. This can help avoid possible interactions between B12 and your other medications.

Give your doctor a complete medical history. B12 may not be right for people with certain medical conditions such as kidney disease, Leber’s hereditary optic neuropathy, or alcoholism.

Tell your doctor if you are pregnant, could be pregnant, planning a pregnancy, or breastfeeding an infant. Your doctor will tell you how much B12 to take.

Precautions During Use of B12

Keep all your healthcare appointments while on B12 (cyanocobalamin injections). Your doctor may order certain lab tests to monitor for side effects.

Continue taking the injections even if you feel well. If you stop the injections, your anemia may come back and cause irreversible nerve damage.

If you are taking the oral form of B12, read the prescription label or package label carefully and take only as much B12 as directed.

B12 Drug Interactions

B12 can interact with certain medications and affect how they work. Some medicines can prevent the normal intestinal absorption of B12 and lead to a deficiency. Possible interactions between B12, other medications, and other dietary supplements can increase the risk of severe adverse reactions.

The following medications may have interactions with B12:

Antibiotics such as chloramphenicol.
Anti-gout medications like colchicine.
Folic acid.
Methotrexate (Trexall, Rheumatrex), a medicine used to treat cancer and autoimmune conditions.
Tuberculosis medications like para-aminosalicylic acid (Paser).
Anti-malarial drugs like pyrimethamine (Daraprim).

The above list may not include all possible interactions of B12. Give your doctor or pharmacist a complete list of your medications, including prescription and nonprescription medications, dietary supplements, and herbal remedies. Also, tell your healthcare professionals if you smoke, drink alcohol, or use recreational drugs because some of these substances can cause serious health complications when used with medications and vitamin supplements.

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