Key points
B6 is needed for protein metabolism. Vitamin B6 helps enzymes process amino acids: it is needed to make serotonin, taurine and carnitine, and with B12 and folic acid it lowers homocysteine (Burgerstein, Handbuch Nährstoffe 2015, p. 77–78, 178, 193, 201).
It may ease nausea in pregnancy. In a randomized trial in 342 women up to 17 weeks pregnant, 30 mg of B6 a day reduced nausea more than placebo did (Vutyavanich T Am J Obstet Gynecol 1995. PMID 7573262).
In PMS, benefit is possible. In a review of 9 studies (940 women), B6 relieved the symptoms of premenstrual syndrome (PMS) more often than placebo, but the quality of most studies is low (Wyatt KM BMJ 1999. PMID 10334745).
Excess B6 harms nerves. Too much B6 causes sensory peripheral neuropathy — damage to the nerves that carry sensation, so the European Food Safety Authority (EFSA) has set an upper level of 12 mg a day for adults (Turck D EFSA J 2023. PMID 37207271).
Symptoms often go away after stopping. Of 172 women with raised B6, 103 had symptoms; in them, at doses of about 100 mg, the symptoms went away within 6 months after stopping (Dalton K Acta Neurol Scand 1987. PMID 3630649). At gram doses only improvement has been described (Schaumburg H N Engl J Med 1983. PMID 6308447).
Why the body needs B6
In the body, vitamin B6 (pyridoxine) is converted into pyridoxal 5′-phosphate (PLP), a helper for enzymes that rearrange amino acids. According to Burgerstein’s handbook, B6 is needed to make serotonin from tryptophan (p. 178), taurine (p. 193), carnitine (p. 201) and glutathione, the cell’s antioxidant (p. 189, 200) (Burgerstein, Handbuch Nährstoffe 2015).
Together with B12 and folic acid, B6 lowers homocysteine (Burgerstein, Handbuch Nährstoffe 2015, p. 77–78), a possible risk factor for heart and blood vessel disease (Martí-Carvajal AJ Cochrane Database Syst Rev 2017. PMID 28816346). On B12 deficiency, see B12 deficiency: symptoms, who is at risk and how it is replenished.
Who may be short of it
B6 status is assessed by PLP in blood plasma; it was used to set the recommended intake in the US, which is no higher than 2 mg a day for any group. In the US National Health and Nutrition Examination Survey (NHANES, more than 6,000 people), low PLP was found more often in these groups (Morris MS Am J Clin Nutr 2008. PMID 18469270):
Women taking contraceptives. Most women on oral contraceptives had PLP below 20 nmol/L (4.9 ng/mL), and women of childbearing age overall had lower levels than men of the same age (Morris MS Am J Clin Nutr 2008. PMID 18469270).
Smokers and older people. In these groups, low PLP occurred in more than 3% even at 3–4.9 mg of B6 a day — above the recommended intake (Morris MS Am J Clin Nutr 2008. PMID 18469270).
Where B6 helps
Nausea in early pregnancy. 342 women up to 17 weeks pregnant received 30 mg of B6 a day or placebo for 5 days. Nausea decreased more on B6; so did vomiting, but the difference was not significant (Vutyavanich T Am J Obstet Gynecol 1995. PMID 7573262). In a Cochrane review of all methods (41 trials, 5,449 women), the evidence for B6 in mild and moderate nausea and vomiting is limited — but this does not mean the remedies do not work (Matthews A Cochrane Database Syst Rev 2015. PMID 26348534). The 30 mg dose is above the EFSA upper level of intake, so in pregnancy B6 is taken only in agreement with a doctor.
Premenstrual syndrome. In a systematic review of 9 studies with 940 women, the odds of improvement in PMS symptoms on B6 were 2.32 times higher than on placebo. But the quality of most studies is low, and the authors link the benefit to doses of up to 100 mg a day (Wyatt KM BMJ 1999. PMID 10334745) — 8 times higher than the current EFSA upper level of intake, so such a dose should not be chosen on your own.
Why too much B6 harms nerves
In 1983, 7 adults who took large daily doses of pyridoxine were described: they developed an unsteady gait (ataxia) and severe sensory impairment, in four of them with severe disability. After B6 was stopped, all of them improved (Schaumburg H N Engl J Med 1983. PMID 6308447).
In a prospective study, 5 healthy volunteers received 1 or 3 g of B6 a day; at the higher dose, symptoms appeared sooner. After stopping, the symptoms kept getting worse for another 2–3 weeks, although PLP in the blood had already returned to normal (Berger AR Neurology 1992. PMID 1620347).
Neuropathy also occurs at much lower doses. In a series of 172 women with raised blood B6, 103 (60%) had symptoms. Their average dose was 117 mg a day, the same as in women without symptoms (116 mg); what differed was the duration of intake: 2.9 years versus 1.6 years. The symptoms went away within 6 months after stopping, and in 4 women they returned when B6 was taken again (Dalton K Acta Neurol Scand 1987. PMID 3630649).
The upper level is 12 mg a day. In 2023 EFSA named peripheral neuropathy as the main risk of excess B6. The starting point — 50 mg a day, based on a case–control study and case reports — was reduced 4-fold because of insufficient data and because at lower doses symptoms appear later. This gave 12.5 mg; taking a second calculation into account, EFSA rounded it to 12 mg a day for adults, including pregnant and breastfeeding women. This level is usually exceeded by people who regularly take high-dose B6 supplements (Turck D EFSA J 2023. PMID 37207271).
The Australian experience. Products with more than 100 mg of B6 were taken off the market there in 2023, and products from 50 mg are being moved to sale through a pharmacist (the transition period is still under way), but in almost 8% of purchases several B6 products were bought at once (Chan WJ Intern Med J 2026. PMID 42503003).
How to recognize it. Tingling, numbness, increased skin sensitivity, bone pain, muscle twitching — most pronounced in the hands and feet, usually on both sides (Dalton K Acta Neurol Scand 1987. PMID 3630649); in severe cases, an unsteady gait (Schaumburg H N Engl J Med 1983. PMID 6308447). Muscle weakness was described in one series; in another, it was absent.
What the studies showed
| What was studied | Who took part | Result |
|---|---|---|
| Pregnancy nausea, 30 mg a day, 1995 | 342 women up to 17 weeks | Nausea decreased more than on placebo; no significant difference in vomiting |
| Pregnancy nausea, Cochrane review of all methods, 2015 | 41 trials, 5,449 women | Evidence for B6 in mild and moderate nausea and vomiting is limited |
| PMS, systematic review, 1999 | 9 studies, 940 women | Odds of improvement 2.32 times higher; low study quality |
| Folic acid, B12 and/or B6 supplements, separately or together, Cochrane review, 2017 | 15 trials, 71,422 people | No fewer heart attacks or deaths; stroke 4.3% vs 5.1% |
| Neuropathy, case reports, 1983 | 7 adults | All improved after stopping |
| Neuropathy, case series, 1987 | 172 women with high B6 | Symptoms in 103, average dose 117 mg; went away within 6 months |
| EFSA upper level, 2023 | Systematic reviews | 12 mg a day for adults, including pregnant women |
Who should be more careful
- People taking several supplements: B6 is found in B-complex products, multivitamins and magnesium with B6 — add up the doses from all the labels.
- People taking B6 for months or years: not only the dose matters, but also how long it is taken (Dalton K Acta Neurol Scand 1987. PMID 3630649).
- Pregnant and breastfeeding women: the upper level of 12 mg a day applies to them too (Turck D EFSA J 2023. PMID 37207271).
- If you have tingling or numbness in your hands and feet: stop B6 supplements and see a doctor. B12 deficiency causes similar symptoms, so a blood test will help sort it out.
Bottom line
B6 is needed for amino acid metabolism, and in studies it eased nausea in pregnancy and, probably, PMS symptoms. But taking large doses for a long time damages nerves, and EFSA has set an upper level of intake of 12 mg a day. After stopping, symptoms often go away: at doses of about 100 mg within 6 months, while at gram doses only improvement has been described. The dose and duration can be chosen at a consultation.
This material is for information only and does not replace a consultation with a doctor. The dose and duration of B6 are chosen by a doctor, taking into account all the supplements you take.
