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 cobalamin, cobalt, or any other product ingredients.
Side Effects and Warnings
Vitamin B12 is generally considered safe when taken in amounts that are not higher than the recommended dietary allowance (RDA). There are not enough scientific data available about the safety of larger amounts of vitamin B12 during pregnancy or breastfeeding.
Use cautiously in patients with cardiovascular concerns. After coronary stenting, an intravenous loading dose of folic acid, vitamin B6, and vitamin B12 followed by oral administration daily has been shown to increase rates of restenosis (reoccurrence of narrowing of a blood vessel). Due to the potential for harm, this combination of vitamins should not be recommended for patients receiving coronary stents.
Use cautiously in patients with elevated blood pressure, as high blood pressure following intravenous administration of hydrocobalamin has been reported.
Use cautiously in patients with dermatologic concerns, as pustular or papular rash, pruritus, and erythema have been reported. Vitamin B12 and pyridoxine have been associated with cases of rosacea fulminans, characterized by intense erythema with nodules, papules, and pustules. Symptoms may persist for up to four months after the supplement is stopped and may require treatment with systemic corticosteroids and topical therapy. Pink or red skin discoloration has also been reported.
Use cautiously in patients with genitourinary concerns, as urine discoloration has been reported.
Use cautiously in patients with gastrointestinal concerns, as nausea, difficulty swallowing, and diarrhea have been reported.
Use cautiously in patients with hematological concerns, as, according to case report data, treatment of vitamin B12 deficiency may lead to polycythemia vera, which is characterized by an increase in blood volume and the number of red blood cells.
Use cautiously in patients with subnormal serum levels of potassium, as the correction of megaloblastic anemia with vitamin B12 may result in fatal hypokalemia in susceptible individuals.
Use cautiously in patients with a history of gout, or elevated uric acid levels, as the correction of megaloblastic anemia with vitamin B12 may precipitate gout in susceptible individuals.
Use cautiously in patients taking the following agents, as they have been associated with reduced absorption or reduced serum levels of vitamin B12: ACE inhibitors, acetylsalicylic acid (aspirin), antibiotics, anticonvulsants, bile acid sequestrants, colchicine, H2 blockers, metformin, neomycin, nicotine, nitrous oxide, oral contraceptives, para-aminosalicylic acid, potassium chloride, proton pump inhibitors (PPIs), and zidovudine (AZT, Combivir®, Retrovir®). Additionally, vitamin C may cause the degradation of vitamin B12 in multivitamin supplements, and chloramphenicol may inhibit the biosynthesis of vitamin B12.
Avoid in patients sensitive or allergic to cobalamin, cobalt, or any other vitamin B12 product ingredients.
Pregnancy and Breastfeeding
Vitamin B12 is likely safe when used orally in amounts that do not exceed the recommended dietary allowance (RDA). There is insufficient reliable information available about the safety of larger amounts of vitamin B12 during pregnancy.