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Vitamin B6 (Pyridoxine)

Vitamin B6 has genuine, specific uses — nausea in pregnancy, isoniazid-induced neuropathy, and possibly PMS — but it is also the one water-soluble vitamin with well-documented nerve toxicity at doses people routinely buy over the counter.

What the science says

  • Reduces nausea and vomiting of pregnancy Strong evidence

    Pyridoxine 10-25 mg every 6-8 hours, alone or combined with doxylamine, is first-line therapy for nausea and vomiting of pregnancy in ACOG and Canadian obstetric guidance, based on randomised trials showing reduced nausea scores versus placebo. The doxylamine-pyridoxine combination is an approved prescription product in several countries.

  • Improves premenstrual syndrome symptoms Moderate evidence

    A systematic review of nine placebo-controlled trials (940 women) found B6 up to 100 mg/day roughly doubled the odds of overall PMS symptom improvement (OR ~2.3) and of depressive symptom improvement (OR ~1.7). The authors flagged low methodological quality across the included trials, so treat the effect size as soft.

  • Prevents isoniazid-induced peripheral neuropathy Strong evidence

    Isoniazid depletes pyridoxal phosphate, and co-administration of pyridoxine 25-50 mg/day is standard tuberculosis practice to prevent the resulting neuropathy. This is an established pharmacological indication rather than a nutritional one.

  • Is harmless at high doses Limited evidence

    Chronic intake above roughly 50 mg/day — and clearly above 200 mg/day — can cause a dose- and duration-dependent sensory peripheral neuropathy with numbness, ataxia and burning pain. Cases have been reported at doses well within the range sold on shelves, and recovery after stopping is usually but not always complete. Several regulators have moved to cap over-the-counter B6 content for this reason.

Dosage & safety

Studied doseRDA is 1.3 mg/day for adults under 50, rising to 1.7 mg (men) and 1.5 mg (women) after 50. Nausea of pregnancy: 10-25 mg every 6-8 hours. PMS trials used 50-100 mg/day. Isoniazid prophylaxis: 25-50 mg/day. Tolerable upper limit for adults is 100 mg/day, and there is little reason to exceed 50 mg/day for long periods. Pyridoxal-5'-phosphate (P5P) is often marketed as safer, but elimination of neuropathy risk with chronic high dosing has not been demonstrated.
SafetyDose-dependent sensory peripheral neuropathy is the defining risk — numbness, tingling, gait unsteadiness — reported with chronic use above ~50 mg/day and well documented above 200 mg/day. Discontinue immediately and seek medical review if these appear. B6 reduces levodopa efficacy when levodopa is given without carbidopa, and may lower phenytoin and phenobarbital levels. Observational data link long-term high-dose B6 (with B12) to increased hip fracture risk and, in male smokers, to lung cancer. Pregnancy doses in the 10-75 mg/day range are considered safe and are guideline-endorsed. Check multivitamins and 'energy' or 'nerve support' products — stacked B6 doses add up quickly.

Scientific references

Where to buy

Swanson Vitamins, Vitamin B6 Pyridoxine, 100 mg, 250 Vegan Capsules

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