The most common supplemental form of vitamin B6, converted in the liver to the active cofactor pyridoxal 5-phosphate. It participates in well over a hundred enzyme reactions, most in amino-acid metabolism.
Vitamin B6 is the vitamin most likely to cause real, lasting harm from ordinary over-the-counter use, and the harm is the opposite of what people expect: too much causes a sensory peripheral neuropathy — numbness, burning and unsteadiness in the hands and feet — that may not fully resolve after stopping. Classic cases involved grams a day, but reports at far lower chronic intakes accumulated to the point that EFSA revised its upper limit down to 12 mg/day in 2023, and Australia now requires warning labels on products supplying more than 10 mg. Meanwhile many B-complex and "energy" products contain 50–100 mg per tablet. Its genuine uses are narrow: deficiency correction, isoniazid-induced neuropathy, and nausea in pregnancy, where a specific low-dose combination is well established.
Sold as
Tablet, Capsule, Slow-release tablet, Component of B-complex and energy formulas, Doxylamine–pyridoxine combination (prescription)
Regulation: The IOM set a Tolerable Upper Intake Level of 100 mg/day; EFSA reduced its own to 12 mg/day in 2023 after reassessing the neuropathy evidence. Australia's regulator requires a warning statement on products supplying more than 10 mg/day. Products supplying 50–100 mg remain widely sold in the US.
What the research used
The amounts, forms and durations published trials of Vitamin B6 (pyridoxine) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Recommended Dietary Allowance, adults
1.3–1.7 mg
Strong
1.3 mg/day for most adults, rising to 1.5 mg for women and 1.7 mg for men over 50. Note how far this sits below the 50–100 mg tablets sold routinely.
Studied for Tolerable Upper Intake Level
12–100 mg
Strong
The two major bodies disagree: EFSA set 12 mg/day in 2023, the IOM 100 mg/day. The gap reflects how seriously each weighted case reports of neuropathy at moderate chronic doses. The lower figure is the more cautious reading of the same literature.
Studied for Nausea and vomiting of pregnancy
10–25 mg
Moderate
Every 8 hours, often combined with doxylamine
A well-established obstetric use with trial support, at doses far below the harmful range. The doxylamine–pyridoxine combination is a licensed medicine in several countries.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
None of the timings below were directly compared in a trial. They reflect how the research happened to dose, or what the pharmacology implies — which is not the same as a timing being better.
🌅Morning
Not enough
Conventionally taken in the morning with other B vitamins. No comparative timing trial exists; this is habit.
Timing was not directly compared. This reflects convention or how the compound behaves in the body, not a trial showing this window works better.
The evidence in depth
Best supported: Moderate
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Low-dose pyridoxine reduces nausea in early pregnancy in randomised trials, alone and in combination with doxylamine, and is recommended as a first-line option in several obstetric guidelines. The doses used are modest and well below the range associated with nerve damage.
Moderate evidence. Several human studies point the same way, with real caveats.
Meta-analysis · The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians · 2022 · PMID 31937153
B6 lowers homocysteine as part of B vitamin combinations, but the large homocysteine-lowering trials found no reduction in cardiovascular events. This is a well-replicated null.
Not enough evidence. Not enough human research to say anything useful yet.
No source is attached to this association yet, so it is rated not enough evidenceby default. It is listed because people commonly ask about it — not because there is evidence for it.
Evidence is limited for vitamin B6 and premenstrual symptoms or mood. Reviews describe the trials as small and of poor quality, and the doses commonly recommended in the popular literature approach the range associated with neuropathy.
Not enough evidence. Not enough human research to say anything useful yet.
Randomised controlled trial · Stress and health : journal of the International Society for the Investigation of Stress · 2021 · PMID 33864354
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Irreversible sensory peripheral neuropathy
Sustained high intake damages sensory nerves, producing numbness, burning pain, tingling and loss of position sense that can make walking unsteady. The classic cases involved 2–6 g/day, but published reports describe it at intakes closer to 50 mg/day taken for long periods. Recovery after stopping is often partial and sometimes does not occur at all. This is the single most important fact about vitamin B6 supplements and it appears on almost no label in the US.
Too much
Doses in ordinary products routinely exceed the upper limit
B-complex, "energy", "stress" and premenstrual formulas commonly contain 50–100 mg of B6 per tablet, against an RDA of 1.3 mg and a European upper limit of 12 mg/day. Stacking two such products is easy and unremarkable-looking. Checking the B6 content of everything being taken at once is worth doing.
Interaction
Reduces the effect of levodopa and interacts with several drugs
Pyridoxine accelerates peripheral breakdown of levodopa, reducing its effect in Parkinson disease when levodopa is taken without a decarboxylase inhibitor. It also reduces blood levels of phenytoin and phenobarbital. In the other direction, isoniazid, hydralazine, penicillamine and cycloserine deplete B6 — the reason pyridoxine is co-prescribed with isoniazid.
Worth knowing
Symptoms can be mistaken for the problem being treated
People take B6 for tingling and nerve symptoms, and high-dose B6 causes tingling and nerve symptoms. Escalating the dose in response to worsening symptoms is a documented pattern and makes the outcome worse.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.