Vitamin B6 (pyridoxine vs P5P)
Summary
Most supplements contain pyridoxine hydrochloride; some contain the active coenzyme PLP (P5P). ODS reports absorption does not differ substantially between forms. Trials found less nausea in early pregnancy and small premenstrual symptom gains in low-quality studies. B vitamins did not improve cognition in healthy older adults. Long-term intakes of grams per day can damage nerves.
Key facts
- Pyridoxine hydrochloride (most common); pyridoxal 5'-phosphate (PLP, P5P)[1]
- ODS: absorption from supplements is similar to food and does not differ substantially among forms; large doses are absorbed well but quickly excreted in urine[1]
- Nausea in early pregnancy ↓ (B); premenstrual symptoms ↑ improvement (C, low-quality trials); thinking skills in healthy older adults with B vitamins ↔ (no effect)[3][2][5]
- RDA 1.3 mg (19–50), 1.7 mg men / 1.5 mg women (51+); 1.9 mg pregnancy, 2.0 mg breastfeeding. UL 100 mg/day[1]
- 1–6 g/day for 12–40 months can cause severe, progressive sensory neuropathy; the UL halves the 200 mg/day level studied without harm[1]
- Cycloserine; antiepileptics (valproic acid, carbamazepine, phenytoin); high-dose B6 may lower phenytoin and phenobarbital levels[1]
- 4 graded human outcomes on this page
- October 8, 2026
How it works
EstablishedIn its active form, pyridoxal 5'-phosphate, vitamin B6 is a coenzyme in more than 100 enzyme reactions, mainly in protein metabolism, and is involved in neurotransmitter synthesis, homocysteine metabolism and hemoglobin formation (established). Effects on premenstrual mood symptoms are proposed to relate to its neurotransmitter role (proposed).[1]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Energy | Grade B | Worsened | RCT · n = 342 · 1995 | 2 rows |
| Stress | Grade C | Improved | Systematic review · n = 940 · 1999 | 1 row |
| Focus | No effect | No effect | Systematic review · n = 27,882 · 2018 | 1 row |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Nausea in early pregnancy | Worsened | Grade B | RCT · n = 342 · 1995 Pregnant women at 17 weeks' gestation or earlier, Thailand Form: pyridoxine hydrochloride · Dose: 30 mg/day · Duration: 5 days Nausea scores fell significantly more with pyridoxine than placebo (p = 0.0008). The drop in vomiting episodes did not reach significance (p = 0.0552). | 7573262 (opens PubMed)Source [3] |
| Premenstrual symptoms | Improved | Grade C | Systematic review · n = 940 · 1999 9 published placebo-controlled trials in women with premenstrual syndrome Form: vitamin B6 · Dose: Up to 100 mg/day · Duration: Varied across trials Women were more likely to report overall improvement with B6 than placebo (OR 2.32); depressive symptoms also improved (OR 1.69; 4 trials, 541 women). The authors note most trials were low quality. | 10334745 (opens PubMed)Source [2] |
| Nausea in early pregnancy, by severity | Mixed | Grade D | RCT · n = 59 · 1991 Pregnant women with nausea and vomiting Form: pyridoxine hydrochloride · Dose: 25 mg every 8 hours (75 mg/day) · Duration: 72 hours In women with severe nausea, nausea scores improved more with B6 (4.3 vs 1.8 points). In mild-to-moderate nausea and in the group as a whole there was no significant difference. | 2047064 (opens PubMed)Source [4] |
| Thinking skills in healthy adults in mid and late life (B vitamins) | No effect | No effect | Systematic review · n = 27,882 · 2018 14 trials, mostly adults over 60, many with prior heart or blood-vessel disease Form: folic acid, vitamin B12, vitamin B6, or combinations · Dose: Varied across trials · Duration: Up to 5–10 years B vitamin supplements probably have little or no effect on overall cognitive function up to 5 years (SMD -0.03 to 0.06), and may have none at 5-10 years. | 30556597 (opens PubMed)Source [5] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| Pyridoxine hydrochloride | 82.3%[6] | Absorbed similarly to B6 from food; no substantial difference among forms (ODS).[1] | Sensory neuropathy with chronic high intakes (1–6 g/day); also skin lesions, light sensitivity, nausea and heartburn at excessive intakes.[1] | All trials graded here |
| Pyridoxal 5'-phosphate (PLP, P5P) | Varies[6][1] | No head-to-head human data in our sources; ODS reports absorption does not differ substantially among supplement forms.[1] | No form-specific tolerance data in our sources.[1] | Marketed as the active form; no outcome trials graded here |
Compound weight → elemental active
500 mg pyridoxine hydrochloride ≈ 412 mg elemental active
Studied doses
Doses studied in human trials ranged from 30 to 100 mg/day of pyridoxine in the pregnancy-nausea and premenstrual trials graded here; the pregnancy trials lasted 3 to 5 days and premenstrual trial lengths varied. The adult UL is 100 mg/day.[3][4][2][1]
Intake reference: Adult RDA: 1.3 mg/day (ages 19–50); 1.7 mg for men and 1.5 mg for women 51+; 1.9 mg in pregnancy and 2.0 mg while breastfeeding. Adult UL: 100 mg/day from food and supplements.[1] The FNB halved the 200 mg/day level studied for up to 5 years without neuropathy to set the UL, because long-term harm data are limited. It does not apply to people receiving B6 under medical care. NIH ODS fact sheet (updated June 16, 2023).
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Medicines
- CycloserineNIH fact sheetIncreases urinary loss of pyridoxine, which might worsen the drug's seizures and nerve toxicity; pyridoxine can help offset these effects.[1]
- Phenytoin and phenobarbitalNIH fact sheetPyridoxine at 200 mg/day for 12–120 days can lower blood levels of these drugs; effects of lower amounts are unknown.[1]
Medicines that can lower levels
- Antiepileptic medicinesNIH fact sheetSpeed the breakdown of vitamin B6, lowering plasma PLP and raising homocysteine.[1]
Who should be careful
- Nerve damage at high intakes
- Chronic intakes of 1–6 g/day for 12–40 months can cause severe, progressive sensory neuropathy, and some reports describe it below 500 mg/day. Symptoms usually stop if B6 is stopped when they first appear.[1]
- Pregnancy
- ODS advises pregnant women to consult a physician before B6 supplements for nausea, because amounts used could approach the UL.[1]
- Medicines
- People on antiepileptic medicines or cycloserine should discuss B6 with their clinician.[1]
- Before you start
- Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Articles about Vitamin B6 (pyridoxine vs P5P)
Plain-English answers to common questions, built on the evidence above.
Frequently asked questions
Is P5P better than pyridoxine?
There is no good evidence that it is. ODS reports that absorption does not differ substantially among supplement forms, and we found no head-to-head outcome trials comparing PLP with pyridoxine.[1]
Can vitamin B6 cause nerve damage?
Yes, at high intakes. Long-term use of 1–6 g/day has caused severe sensory neuropathy, and some reports describe it below 500 mg/day. The adult UL is 100 mg/day.[1]
Does B6 help with morning sickness?
In a 342-woman trial, 30 mg/day pyridoxine reduced nausea scores over 5 days, though vomiting did not change significantly. ODS notes a Cochrane review could not draw firm conclusions. Pregnant women should check with their clinician first.[3][1]
Does B6 help premenstrual symptoms?
A 1999 review of 9 trials (940 women) found more women improved with B6 than placebo, but most trials were low quality, so the evidence is weak.[2]
Sources
- [1]Vitamin B6: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2023. fact-sheet
- [2]Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review.. BMJ, 1999. systematic-review
- [3]Pyridoxine for nausea and vomiting of pregnancy: a randomized, double-blind, placebo-controlled trial.. Am J Obstet Gynecol, 1995. RCT
- [4]Vitamin B6 is effective therapy for nausea and vomiting of pregnancy: a randomized, double-blind placebo-controlled study.. Obstet Gynecol, 1991. RCT
- [5]Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life.. Cochrane Database Syst Rev, 2018. systematic-review
- [6]Pyridoxine, pyridoxine hydrochloride and pyridoxal 5'-phosphate: molecular formulas and weights. PubChem, NCBI, 2026. database
What changed
- First draft. Every evidence-row PMID checked with NCBI E-utilities (esummary + efetch abstract) and re-read in an independent adversarial pass.