Vitamin B6, also known as pyridoxine, is an essential vitamin involved in protein metabolism. Deficiency, which is rare, can be induced by the tuberculosis drug isoniazid and manifests as an enlarged and painful tongue. Vitamin B6 toxicity is also rare and occurs in individuals who consume megadoses of vitamin B6, usually as a result of overzealous supplementing or medical treatment. Symptoms are neurologic.

Vitamin B6 is available in pill form, either as part of a multivitamin or on its own. It is a water-soluble vitamin, meaning excess amounts are excreted in the urine. However, long-term supplementation with very high doses may result in painful neurological symptoms, including pins-and-needles sensations, known as sensory neuropathy. To date, no studies have shown toxicity from daily intake at or below 200 mg per day. For safety, the tolerable upper intake level is 100 mg per day. Many supplements include this amount of B6.

Megadoses of vitamin B6 in the amount of 500 mg per day are sometimes used for the treatment of certain conditions. These include carpal tunnel syndrome and premenstrual syndrome. Effectiveness of vitamin B6 for the treatment of any condition is unproven, according to the Merck Manuals Online Medical Library, and since a clear association between megadoses of vitamin B6 and neurologic symptoms exists, risks of supplementation may outweigh the benefits, so ask your doctor.

The recommended dietary allowance is of vitamin B6 is about 1.5 mg per day. Foods contain less vitamin B6 than supplements. Even fortified cereals, which are the highest in B6 of all foods, contain less than 5 mg per serving. Other foods high in B6 include chickpeas and fish. Eating large quantities of these foods is unlikely to produce symptoms of toxicity, since it may be impossible to achieve dietary levels approaching 100 mg per day without supplementation.