The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Vitamin B12 supplements should be avoided in people sensitive or allergic to vitamin B12, cobalt, or any other product ingredient.
Side Effects and Warnings
Vitamin B12 is likely safe when taken according to the recommended dietary amounts (RDA) or less.
Use cautiously in people with heart concerns, due to an increase in rates of restenosis (reoccurrence of narrowing of a blood vessel) after stent placement and vitamin B12 supplementation.
Use cautiously in people with high blood pressure, as high blood pressure following intravenous (IV) administration of hydrocobalamin has been reported.
Use cautiously in people with a history of cancer.
Use cautiously in people with skin disorders, as rash, itching, and burning have been reported. Pink or red skin discoloration and facial flushing have also been reported.
Use cautiously in people with genitourinary concerns, as urine discoloration has been reported.
Use cautiously in people with gastrointestinal concerns, as nausea, difficulty swallowing, and diarrhea have been reported.
Use cautiously in people with blood disorders, as it has been reported that treatment of vitamin B12 deficiency may lead to an increase in blood volume and the number of red blood cells.
Use cautiously in people with low serum levels of potassium, as the correction of megaloblastic anemia with vitamin B12 may result in fatally low potassium levels.
Use cautiously in people with a history of gout, or elevated uric acid levels, as the correction of megaloblastic anemia with vitamin B12 may start a gout attack.
Use cautiously in people taking the following agents, as they have been associated with reduced absorption or reduced serum levels of vitamin B12: ACE inhibitors, acetylsalicylic acid (aspirin), alcohol, antibiotics, anti-seizure agents, bile acid sequestrants, chloramphenicol, colchicine, H2 blockers, metformin, neomycin, nicotine, nitrous oxide, oral contraceptives, para-aminosalicylic acid, potassium chloride, proton pump inhibitors (PPIs), tobacco, vitamin C, and zidovudine (AZT, Combivir®, Retrovir®).
Avoid in people sensitive or allergic to vitamin B12, cobalt, or any other product ingredient.
Pregnancy and Breastfeeding
Vitamin B12 is likely safe when taken according to the recommended dietary amounts (RDA) or less. There is insufficient reliable information available about the safety of larger amounts of vitamin B12 during pregnancy.
Infants, when breastfed by a vitamin B12-deficient mother, are at risk for many health issues such as severe developmental disorders, growth failure, and anemia. Some research has reported that vitamin B12 levels during pregnancy have effects on mental function in infants.
This evidence-based monograph was prepared by The Natural Standard Research Collaboration