Use and abuse of high dosages of vitamin B6

Concepts of vitamin B6 megatherapy are classified in three categories: 1. megatherapy with well-known mechanism of action; 2. megatherapy with hypothetical or unknown, but nevertheless plausible mechanism of action; 3. megatherapy on the basis of pure speculation. Examples of all three categories are shown. The dosages applied extend from 100 mg up to several grams; the duration of treatment varies from weeks to several years. After long-term intake of high doses toxic effects can occur in the form of peripheral sensory neuropathy, in two reported cases combined with a subepidermal vesicular dermatosis. The threshold above which toxic effects can occur appears to be somewhat between 300 and 500 mg/day; however, systematic investigations in this dose range have never been performed. Furthermore, there appears to be an inverse relationship between the dose and the time up to the occurrence of toxic symptoms. The danger consists less in controlled application by a physician as far as he is aware of the clinical picture of sensory neuropathy. Doses in excess of 500 mg are rarely necessary in specific indications. Unlike this situation, self-medication by laymen on the basis of promises in obscure health magazines is much more risky because the dose is frequently raised more and more up to several grams per day when the expected effect does not occur.