If you are currently being treated with any of the following medications, you should not use vitamin B12 supplements without first talking to your health care provider.

Medications that reduce levels of B12 in the body include:

• Anticonvulsants -- include phenytoin (Dilantin), phenobarbital, primidone (Mysoline)
• Chemotherapy medications -- particularly methotrexate
• Colchicine -- used to treat gout
• Bile acid sequestrants -- used to lower cholesterol; include colestipol (Colestid), cholestyramine (Questran), and colsevelam (Welchol)
• H2 blockers -- used to reduce stomach acid; include cimetidine (Tagamet), famotidine (Pepcid AC), ranitidine (Zantac)
• Metformin (Glucophage) -- medication taken for diabetes
• Proton pump inhibitors -- used to reduce stomach acid; include esomeprazole (Nexium), lansprazole (Prevacid), omeprazole (Prilosec), rabeprazole (Aciphex)

Antibiotics, Tetracycline: Vitamin B12 should not be taken at the same time as tetracycline because it interferes with the absorption and effectiveness of this medication. Vitamin B12 should be taken at different times of the day from tetracycline. (All vitamin B complex supplements act in this way and should be taken at different times from tetracycline.)

In addition, long-term use of antibiotics can deplete vitamin B levels in the body, particularly B2, B9, B12, and vitamin H (biotin), which is considered part of the B complex vitamins.