Vitamin B6 (Pyridoxine)
The cofactor for the transsulfuration route that breaks homocysteine down to cysteine. Deficiency is uncommon, and in meta-analyses B6 adds nothing to fasting homocysteine lowering. Its main modern issue is excess: supplemental B6 causes sensory neuropathy, reported in the Netherlands even from products of 1.4–100 mg per tablet, and the EU upper limit was cut to 12 mg/day in 2023. Use a low dose or none.
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BiohackingHub Research TeamEditorial Research Team · Last updated: October 19, 2026
Medical Disclaimer: The information on this page is for educational and research purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.
What Vitamin B6 Does
As pyridoxal 5'-phosphate, vitamin B6 is the cofactor for over a hundred enzymes, including those making serotonin, dopamine and GABA. In one-carbon metabolism it drives transsulfuration — the one-way breakdown of homocysteine to cysteine and then glutathione. That route matters most after a protein-rich meal, not in the fasting state, which is why B6 barely moves a fasting homocysteine test.
What It Does Not Do: Lower Fasting Homocysteine
The Homocysteine Lowering Trialists' Collaboration pooled 25 randomised trials and found no significant effect of B6 on fasting homocysteine; folic acid and B12 did all the work. In a six-week trial in 100 men with raised homocysteine, folic acid lowered it by 42% and B12 by 15%, while 10 mg of B6 did not lower it significantly. One small trial in older adults found a 7.5% fall with 1.6 mg B6 — but only after folate and riboflavin had been fully repleted first.
The large cardiovascular trials that included B6 did not do better for it. In the NORVIT trial after heart attack, the arm given folic acid, B12 and B6 had a borderline increase in events. Full trial picture in Homocysteine: What Your Level Means and How to Lower It.
The Neuropathy Problem
High-dose B6 is a well-established nerve toxin. The 1983 case series that defined the syndrome described seven adults with disabling sensory neuropathy and ataxia from megadose pyridoxine; all improved after stopping. A prospective study in volunteers showed the damage was dose-dependent and that symptoms continued to worsen for two to three weeks after the last dose.
The modern concern is lower doses. The Dutch pharmacovigilance centre analysed 90 reports of neuropathy linked to supplements containing 1.4–100 mg per tablet, and concluded that harm below 50 mg/day could not be excluded. In 2023 the European Food Safety Authority lowered the adult upper limit to 12 mg/day, including in pregnancy. The US limit remains 100 mg/day, set in 1998. Australia withdrew products above 100 mg and is moving 50 mg-plus products to pharmacist-only supply.
A 2023 systematic review found no proven therapeutic role for B6 in treating neuropathy — the condition it can cause.
Who Might Need It
- Diagnosed deficiency, or long-term use of isoniazid, hydralazine or penicillamine.
- Nausea of early pregnancy — 30 mg/day reduced nausea scores in a 342-woman trial, and a Cochrane review found limited supportive evidence. This is short-term and should be agreed with an obstetric clinician, given the EU upper limit.
Outside those cases, the B6 in a balanced diet and a standard multivitamin is enough.
Where It Fits
B6 is deliberately not a layer of the Methylation Support Protocol. The protocol tells you to count the B6 in everything else you take and keep the total under 12 mg.
Related Research
Stacking Interactions
How Vitamin B6 (Pyridoxine) interacts with other compounds
Low riboflavin status impairs B6 activation
Different homocysteine pathways; B12 is the one that lowers fasting levels
Many magnesium products are sold as 'Mg + B6' — check the label so total B6 stays under 12 mg/day
Safety Profile — Tier B
Generally safe — moderate evidence
Contraindications
- ●Existing peripheral neuropathy or tingling in hands or feet — avoid supplemental B6
- ●Stacking several B6-containing products (multivitamin + B-complex + magnesium-B6) — total intake easily exceeds the EU upper limit
- ●Levodopa taken without carbidopa — B6 reduces its effect
Side Effects
- ●Sensory neuropathy — numbness, tingling, unsteady gait — with long-term high intake; symptoms can keep worsening for 2–3 weeks after stopping ('coasting')
- ●Nausea; photosensitivity rarely