Vitamin B6 (Pyridoxine)
vitamin · also known as pyridoxine, pyridoxine hydrochloride, P5P, P-5-P, pyridoxal-5-phosphate, pyridoxal-5'-phosphate, vitamin B-6, B6
This is general information, not medical advice. Supplements can interact with medicines and health conditions. Always check with your doctor or pharmacist before starting or changing supplements.
What it is
Vitamin B6 is a water-soluble vitamin that the body converts to pyridoxal-5'-phosphate (PLP), the coenzyme for more than 140 enzyme reactions, most of them in amino acid metabolism, along with haemoglobin synthesis and the production of several neurotransmitters. Outright deficiency is uncommon on a normal diet, and B6 is unusual among the B vitamins in that its best-supported supplemental uses are quite specific — nausea and vomiting in early pregnancy, and premenstrual symptoms — rather than the general "energy" benefit these products are usually sold on. It is also the B vitamin with the clearest evidence of harm from taking too much for too long: chronic supplementation can cause a sensory peripheral neuropathy, and the dose at which that becomes a risk is lower and less certain than most labels imply. That risk drove a substantial regulatory divergence in 2023, when the European Food Safety Authority cut its tolerable upper intake level to 12 mg/day for adults, roughly one-eighth of the 100 mg/day figure still in use in the United States. Products advertising the "activated" P5P form as inherently safer are making a mechanistic argument that has not been tested in people.
Which form to choose
Grades here rate how well the evidence supports choosing a form, which is not the same as how much that form has been studied: a well-studied form can be graded low precisely because the studies argue against it. This is a different scale from the claim grades below — see our editorial policy.
The standard and by far the most studied form, and the one used in essentially all of the trials behind the claims below. It is well absorbed in the small intestine and converted to the active coenzyme PLP in the liver. Being water-soluble, excess is largely excreted in urine — but "water-soluble" is not the same as "harmless in excess": the neuropathy risk below is real and accumulates over years.
Graded on trial use. Every benefit this monograph reports was demonstrated with pyridoxine hydrochloride: the nausea-in-pregnancy trials and the premenstrual syndrome review both used it, and no claim here rests on any other form. Held at B rather than A because that reflects the strength of the underlying claims themselves, which are modest, rather than any doubt about which form was used.
The active coenzyme form, marketed as better absorbed and, more pointedly, as avoiding the neuropathy risk that comes with pyridoxine. Neither claim is established in humans. No head-to-head trial comparing oral P5P with pyridoxine hydrochloride for bioavailability or for neurological safety appears in the published literature. The safety argument rests on a cell-culture study in which pyridoxine, but not P5P, killed human neuroblastoma cells, and on review articles repeating that reasoning while explicitly calling for the clinical trials that would test it. Against it: the systematic review of B6 neuropathy frames the risk in terms of raised blood PLP, which is what P5P supplementation directly produces. The absence of published P5P neuropathy cases is more plausibly explained by its much smaller share of the market than by demonstrated safety. Treat the same upper limit and the same duration caution as applying to both forms.
Graded low because the evidence is absent, not because it is negative, and that distinction matters here. No head-to-head trial comparing oral P5P with pyridoxine hydrochloride for absorption or for neurological safety appears in the published literature, so the two claims it is usually sold on are both unestablished in humans. The safety argument rests on cell culture, while the systematic review of B6 neuropathy frames the risk in terms of raised blood PLP, which is exactly what P5P produces. Below pyridoxine because every trial behind this monograph used pyridoxine, and a form with no comparative evidence cannot outrank the one the results came from.
Evidence-based benefits
Vitamin B6, alone or combined with doxylamine, reduces nausea and vomiting symptom scores in early pregnancy compared with placebo, though the size of the benefit is modest and may fall short of what patients would notice as a meaningful change.
A 2026 systematic review and network meta-analysis of 24 randomised controlled trials (3,017 participants across 16 intervention categories) ranked vitamin B6, alone and in combination, among the more effective interventions for nausea and vomiting of pregnancy against placebo, while grading the underlying evidence as low to moderate quality with considerable uncertainty. In a head-to-head randomised trial of 77 women who completed treatment, pyridoxine 40 mg twice daily for four days significantly improved Rhodes nausea and vomiting scores against placebo (p=0.007), performing comparably to ginger 500 mg twice daily. The grade here is B rather than A because of what happened when the pivotal doxylamine-pyridoxine trial (265 women, 10 mg/10 mg two to four times daily for 14 days) was reanalysed: the improvement was 0.73 points (95% CI 0.21-1.25) on a 13-point emesis scale, statistically significant but well below the 3-point difference the trial itself had set in advance as the smallest change that would matter clinically. The effect is real; whether it is large enough to feel is a separate question the evidence does not settle.
- Grade B· Limited evidence[1]
Vitamin B6 at doses up to 100 mg/day may improve overall premenstrual symptoms and premenstrual depressive symptoms compared with placebo, but the trials supporting this are old and mostly of low methodological quality.
A systematic review of nine published placebo-controlled randomised trials (940 women) found an odds ratio of 2.32 (95% CI 1.95-2.54) for improvement in overall premenstrual symptoms with vitamin B6 against placebo, and an odds ratio of 1.69 (95% CI 1.39-2.06) for improvement in premenstrual depressive symptoms specifically across four trials (541 women). The reviewers' own stated conclusion is that "conclusions are limited by the low quality of most of the trials included", which is why this is graded B despite being a pooled analysis of randomised trials. Note also the tension between this result and the safety claim below: the review found doses up to 100 mg/day likely to be of benefit, and 100 mg/day is more than eight times the current European upper intake level. A benefit demonstrated at a dose we would not recommend taking indefinitely is a reason to treat this as short-course, supervised use rather than a daily habit.
- Grade B· Limited evidence[1]
Vitamin B6 does not relieve carpal tunnel syndrome, despite a long history of being recommended for it.
A systematic review of 33 randomised controlled trials of conservative (non-surgical) treatments for electrophysiologically confirmed carpal tunnel syndrome graded the evidence by strength and placed vitamin B6 in the negative column: moderate evidence (level 2) that vitamin B6 is ineffective, alongside moderate evidence that splints are effective and strong evidence (level 1) for local and oral steroids. This claim is listed as a benefit because that is how readers will arrive at it — looking for whether B6 helps their wrists. The honest answer from the pooled trial evidence is that it does not, and taking high-dose B6 for a condition it does not treat is how people accumulate the exposure described in the neuropathy claim above.
- Grade A· Strong evidence[1]
Added to folic acid and vitamin B12, vitamin B6 produces no significant further reduction in blood homocysteine.
A meta-analysis of individual participant data from 12 randomised controlled trials (1,114 people) found folic acid (0.5-5 mg/day) reduced blood homocysteine by 25% (95% CI 23-28%), and adding vitamin B12 at about 0.5 mg/day produced a further 7% reduction (95% CI 3-10%). Vitamin B6, at a mean dose of 16.5 mg/day, produced no statistically significant additional effect. B6 is routinely included in homocysteine-lowering formulations, and on this evidence it is the one of the three doing the least work — which matters because it is also the one of the three with a documented neuropathy risk.
Risks & contraindications
Chronic vitamin B6 supplementation can cause a predominantly sensory, axonal peripheral neuropathy, and no dose has been shown to be safe indefinitely — cases are documented at intakes as low as 6 mg/day, below the current European upper limit.
A 2023 systematic review of 20 studies concluded that raised vitamin B6 levels, usually from supplements, may cause a predominantly and sometimes exclusively sensory neuropathy of the axonal type, with symptoms typically improving after stopping, and that current evidence supports a neurotoxic role for B6 at high levels. The European Food Safety Authority's 2023 opinion setting the upper intake level states plainly that a lowest-observed-effect level could not be established from human data; it derived a reference point of 50 mg/day from a case-control study together with case reports and pharmacovigilance data, applied an uncertainty factor of 4, and set the adult limit at 12 mg/day. A 2023 case report shows why that caution is warranted: a 73-year-old man developed three years of progressive numbness and tingling with a serum B6 of 259.9 nmol/L (reference 20-125) while taking a multivitamin supplying just 6 mg/day — half the new European limit, and a small fraction of the 100 mg/day still permitted in the United States. The grade is C because this rests on case reports, case-control data and pharmacovigilance rather than trials; deliberately dosing people to neuropathy is not a study anyone will run.
- Grade C· Preliminary evidence[1]
Long-term use of high-dose single-ingredient vitamin B6 supplements is associated with roughly double the risk of lung cancer in men, particularly smokers; the association was not seen in women, nor with multivitamins, and an observational cohort cannot establish cause.
The Vitamins and Lifestyle (VITAL) cohort followed 77,118 adults aged 50-76 and identified 808 incident lung cancers through cancer registry linkage, using 10-year average daily supplement dose as the exposure. Vitamin B6 and B12 taken as individual supplements — but not the same vitamins taken in a multivitamin — were associated with a 30-40% increase in lung cancer risk in men, with no association in women. At the highest 10-year average doses the risk in men was close to double: hazard ratio 1.82 (95% CI 1.25-2.65) for B6 above 20 mg/day, and 1.98 (95% CI 1.32-2.97) for B12 above 55 mcg/day, against non-users. Risk was higher still among men smoking at baseline, and was present across histological types except adenocarcinoma, the type least associated with smoking. This is a single observational cohort and the pattern may reflect something about who takes high-dose single B vitamins rather than the vitamins themselves, which is why it is graded C — but the authors' conclusion, that B vitamin supplements are not chemopreventive for lung cancer and may be harmful, is worth reading alongside the marketing.
Dosage & how to take it
- Pyridoxine hydrochloride: 5–12 mg/day, any time of day, with or without food. The range runs from comfortably above the adult reference intake of 1.3-1.7 mg/day up to the European Food Safety Authority's 2023 tolerable upper intake level of 12 mg/day. We have taken the European figure deliberately, and it is worth being explicit that this is a choice: the United States upper limit remains 100 mg/day, set in 1998, and South African product labels may reference either. The two differ by more than eightfold, and the 2023 case of neuropathy at 6 mg/day sits below both. Where a trial supports a higher dose — up to 100 mg/day for premenstrual symptoms, around 40-80 mg/day for nausea in pregnancy — those are short courses of days to weeks, and belong under supervision rather than in an indefinite daily regimen. No duration limit is set here because none can be honestly derived: EFSA states that a lowest-observed-effect level could not be established from human data, so a specific number of days would be invented rather than cited. The real guidance is to keep the dose low and to stop and seek advice if numbness or tingling appears in the hands or feet.
- Pyridoxal-5'-phosphate (P5P): 5–12 mg/day, any time of day, with or without food. Identical to pyridoxine hydrochloride, and deliberately so. Upper intake levels are set for total vitamin B6 regardless of which form it arrives as, and no human evidence supports treating P5P as safer at an equivalent dose. If you are choosing P5P specifically because a label told you it avoids the neuropathy risk, that claim has not been tested in people — see the note on this form above.
Interactions
No interactions in our database yet. We check against a limited set of medications. Absence of a warning is not evidence of safety.
Our medication coverage is not exhaustive. Absence of a warning here is not evidence of safety. Always confirm with your pharmacist.
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