If you are being treated with any of the following medications, you should not use vitamin B6 supplements without first talking to your health care provider.

Drugs that reduce levels of B6 in the body -- If you take any of these medications, be sure to get enough B6 in your diet:

• Cycloserine (Seromycin), used to treat tuberculosis
• Hydralazine (Apresoline), used to treat high blood pressure
• Isoniazid, used to treat tuberculosis
• Penicillamine, used to treat rheumatoid arthritis
• Theophylline (TheoDur), used to treat asthma

Antibiotics, Tetracycline -- All B complex vitamins, including vitamin B6, interfere with the absorption and effectiveness of antibiotic tetracycline. You should take tetracyclien at different times from vitamin B6 and other B vitamins.

Antidepressant Medications -- Taking vitamin B6 supplements may improve the effectiveness of certain tricyclic antidepressants such as nortriptyline (Pamelor), especially in elderly people. Other tricyclic antidepressants include amitriptyline (Elavil), desipramine (Norpramin), and imipramine (Tofranil).

On the other hand, antidepressants called monoamine oxidase inhibitors (MAOIs) may reduce blood levels of vitamin B6. Examples of MAOIs include phenelzine (Nardil) and tranylcypromine (Parnate).

Chemotherapy drugs -- Vitamin B6 may reduce certain side effects of 5-fluorouracil and doxorubicin, medications used to treat cancer, without reducing the effectiveness of the chemotherapy. Talk to your doctor before taking any supplement if you are undergoing chemotherapy.

Erythropoietin (EPO) -- Erythropoietin therapy, used to treat severe anemia, may decrease vitamin B6 levels in red blood cells and may require B6 supplementation.

Levodopa (L-dopa) -- Vitamin B6 reduces the effectiveness of levodopa, a medication used to treat Parkinson's disease. However, your doctor may be able to determine a dose of B6 that can help reduce side effects of levodopa without interfering with the drug's action. Taking vitamin B6 along with levodopa should be done only under the strict guidance of a physician.

Phenytoin (Dilantin) -- Vitamin B6 reduces the effectiveness of phenytoin, a medication used to treat seizures.