Analgesic effects of B vitamins: A review

B vitamins have been used as analgesic drugs to treat pain disorders associated with their deficiency. However, more recently it has been claimed that, at pharmacological doses, B vitamins are useful to relieve different pain states as carpal tunnel, migraine and premenstrual tension. Experiments in animals have shown that vitamins B₁ (thiamine), B₆ (pyridoxine) and B₁₂ (cyanocobalamin) and their combination have antinociceptive activity against chemical- and heat-induced pain. An anti-inflammatory effect has also been reported using the carrageenin-induced edema test. Moreover, the individual administration of thiamine and pyridoxine produce antinociception in acetic acid-induced pain or pain induced by supramaximal electrical stimulation of afferent C fibers. However, the most important effect of B vitamins is related with its use in patients with neuropathic pain. B vitamins have been useful in some painful disorders such as polyneuropathy, neuralgia, radiculopathy, neuritis associated with pain paresthesias, and diabetic peripheral neuropathy. This use has been supported recently by preclinical studies showing the efficacy of these vitamins in well established models of neuropathic pain in rats. The neurophysiological mechanisms induced by B vitamins are still unknown. However, in the last years it has been postulated that B vitamins-induced antinociception could result from activation of opioid receptors or nitric oxide release.