Home Ingredients P-5-P (Pyridoxal-5-Phosphate / Active B6)
Women's Health

P-5-P (Pyridoxal-5-Phosphate / Active B6)

Evidence Level
Moderate
2 Clinical Trials
5 Documented Benefits
3/5 Evidence Score

P-5-P (pyridoxal-5-phosphate, PLP) is the coenzyme form of vitamin B6 that cells use in more than 140 enzyme reactions. Note that swallowed P-5-P is not absorbed intact: intestinal alkaline phosphatase strips the phosphate off to pyridoxal before absorption, and the body re-phosphorylates it inside cells, reaching the same endpoint as plain pyridoxine HCl. No human trial shows P-5-P raises B6 activity faster or better than pyridoxine in healthy people. It is distinct from pyridoxine HCl (the most common synthetic form) and pyridoxamine.

Studied Dose 25–100 mg/day general; 50–100 mg/day for PMS; up to 200 mg/day short-term; UL 100 mg/day.
Active Compound Pyridoxal-5-Phosphate (PLP / P-5-P).

Benefits

Bioactive Coenzyme Form

P-5-P is the coenzyme form of B6. Swallowed P-5-P is dephosphorylated in the gut to pyridoxal before it is absorbed, so it does not bypass the body's phosphorylation steps the way it is marketed to. Healthy adults convert pyridoxine HCl efficiently, and no human trial shows P-5-P works better for them. A theoretical edge for people with impaired phosphorylation (some liver disease or genetic variants) has not been demonstrated in trials.

Supported by Trial 1

Neurotransmitter Synthesis

B6 (as PLP) is cofactor for amino acid decarboxylases that synthesize: serotonin (from 5-HTP), dopamine (from L-DOPA), GABA (from glutamate), histamine (from histidine), epinephrine, and norepinephrine. This is biochemistry: it explains why severe B6 deficiency impairs these pathways, but it is not evidence that B6 supplements improve mood in people who are not deficient, and no standalone depression or mood trial of B6 is cited here.

Supported by Trial 1

Premenstrual Syndrome (PMS)

Vitamin B6 supplementation (50-100 mg/day) modestly improves PMS symptoms — systematic review showed benefit; ACOG mentions B6 as option for PMS. P-5-P or pyridoxine HCl both used.

Supported by Trial 1

Morning Sickness / Nausea of Pregnancy

Vitamin B6 (10-25 mg three times daily) is first-line pharmacologic treatment for nausea and vomiting of pregnancy per ACOG. Often combined with doxylamine (Diclegis® / Diclectin®) for synergistic effect. Pyridoxine HCl is the studied form; P-5-P comparable.

Supported by Trial 2

Homocysteine Lowering

B6 (PLP) is a cofactor for cystathionine beta-synthase, which converts homocysteine to cystathionine. Adequate B6, folate, and B12 keep homocysteine levels lower. Important caveat: large randomized trials that lowered homocysteine with B vitamins (for example HOPE-2 and VISP) did not reduce heart attacks or strokes, so lowering this blood marker has not translated into fewer cardiovascular events.

Supported by Trial 1

Mechanism of action

1

Coenzyme for >140 Enzymes

PLP is cofactor for: amino acid transaminases (ALT, AST — clinical liver enzymes), amino acid decarboxylases (neurotransmitter synthesis), glycogen phosphorylase (glycogen breakdown), heme synthesis (delta-ALA synthase), cystathionine beta-synthase (homocysteine metabolism), kynureninase (tryptophan catabolism).

2

Phosphorylation Bypass

Pyridoxine HCl → pyridoxal → P-5-P requires liver pyridoxine kinase. P-5-P is already phosphorylated — directly usable. Practical advantage modest for healthy adults; may matter in liver disease, alcohol abuse, certain enzyme variants.

3

Neurotransmitter Decarboxylase Cofactor

Critical for: 5-HTP → serotonin; L-DOPA → dopamine; glutamate → GABA; histidine → histamine. B6 deficiency impairs all these pathways simultaneously.

4

Heme Synthesis

PLP is cofactor for delta-aminolevulinic acid synthase — first and rate-limiting step of heme biosynthesis. B6 deficiency causes sideroblastic anemia.

Clinical trials

1
Vitamin B6 for Premenstrual Syndrome
PubMed

Randomized crossover trial of pyridoxine (vitamin B6) for premenstrual syndrome (Doll 1989), consistent with a later systematic overview that lists B6 among options with modest supporting evidence.

Women with premenstrual syndrome in a randomized crossover trial.

B6 (50-100 mg/day) modestly improved PMS symptoms vs placebo. Effect size modest. ACOG recognizes as treatment option. Higher doses (>200 mg) carry neuropathy risk without proportional benefit.

2
Pyridoxine for Pregnancy Nausea — ACOG Recommendation
PubMed

Randomized, double-blind, placebo-controlled trial of pyridoxine for nausea and vomiting of pregnancy (Vutyavanich 1995); pyridoxine is an ACOG-recommended first-line treatment for these symptoms.

Pregnant women with NVP.

Pyridoxine effectively reduces NVP vs placebo. Combined with doxylamine (Diclegis®) for additive effect. Safe in pregnancy at recommended doses.

Side effects and drug interactions

Common Potential side effects

Peripheral neuropathy at chronic high doses (>200 mg/day for months) — sensory neuropathy with paresthesias, ataxia; classically from megadose pyridoxine supplementation; can be irreversible if not caught early.
GI distress at high doses.
Photosensitivity (rare).
Skin rash (rare).
Headache.
Sleep disturbance / vivid dreams in sensitive individuals.

Important Drug interactions

Levodopa / L-DOPA (without carbidopa) — B6 increases peripheral conversion of L-DOPA to dopamine, reducing brain delivery; contraindicated with un-supplemented L-DOPA; not an issue with carbidopa-levodopa (Sinemet) which has peripheral decarboxylase inhibitor.
Phenytoin, phenobarbital — B6 may modestly reduce serum levels; monitor.
Cycloserine — B6 antagonist; supplementation often given alongside.
Hydralazine — B6 antagonist.
Isoniazid — B6 antagonist; B6 supplementation routine in TB treatment.
Penicillamine — B6 antagonist.
Theophylline — B6 may interact.
Contraceptives — modestly reduce B6 status.

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Frequently asked questions about P-5-P (Pyridoxal-5-Phosphate / Active B6)

What is P-5-P (pyridoxal-5-phosphate)?

P-5-P is the active, coenzyme form of vitamin B6 that the body uses directly, without the conversion step that plain pyridoxine requires. It is favored by those who prefer an active vitamin form or have conversion difficulties.

Is P-5-P better than regular vitamin B6?

Both raise B6 activity for most people. P-5-P is already in the active form, which some prefer, especially people with liver or conversion issues, while pyridoxine is cheaper and effective. The practical difference is usually small.

How much P-5-P should I take?

B6 needs are about 1.3 to 1.7 mg per day; supplements provide more. As with all B6, avoid very high long-term doses (generally above 100 mg per day), which can cause nerve problems, even with the active form.

What is P-5-P used for?

Like vitamin B6 generally, it supports amino acid metabolism, neurotransmitter production, and red blood cell formation, and is used for PMS and for nausea of pregnancy, where controlled trials support it. Claims about mood rest on its role in neurotransmitter chemistry rather than on mood trials of the supplement itself.

What is P-5-P?

P-5-P (pyridoxal-5-phosphate, PLP) is the coenzyme form of vitamin B6 that cells use in more than 140 enzyme reactions. Note that swallowed P-5-P is not absorbed intact: intestinal alkaline phosphatase strips the phosphate off to pyridoxal before absorption, and the body re-phosphorylates it inside cells, reaching the…

What is the recommended dosage of P-5-P?

The clinically studied dose is 25–100 mg/day general; 50–100 mg/day for PMS; up to 200 mg/day short-term; UL 100 mg/day. Always follow the product label and check with a healthcare provider for personal advice.

Is P-5-P safe, and does it have side effects?

For most healthy adults, P-5-P is well tolerated at studied doses. Reported effects can include: Peripheral neuropathy at chronic high doses (>200 mg/day for months) — sensory neuropathy with paresthesias, ataxia; classically from megadose pyridoxine supplementation; can be irreversible if not caught early. GI distress at high doses. It may also interact with some medications. P-5-P is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does P-5-P interact with any medications?

Possible interactions include: Levodopa / L-DOPA (without carbidopa) — B6 increases peripheral conversion of L-DOPA to dopamine, reducing brain delivery; contraindicated with un-supplemented L-DOPA; not an issue with carbidopa-levodopa (Sinemet) which has peripheral decarboxylase inhibitor. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for P-5-P?

NutraSmarts rates the evidence for P-5-P as Moderate (3 out of 5). It is backed by 2 clinical trials and 6 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(6 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Doll H, Brown S, Thurston A, Vessey M. Pyridoxine (vitamin B6) and the premenstrual syndrome: a randomized crossover trial. J R Coll Gen Pract. 1989;39(326):364-8..PubMedUsed to support: Randomized crossover trial reporting that vitamin B6 (pyridoxine) relieved premenstrual syndrome symptoms. The trial used pyridoxine HCl, not P-5-P specifically. Supports the women's-health use; the PMS effect is modest and later reviews rate the overall evidence as low quality.
  2. Kashanian M, Mazinani R, Jalalmanesh S, Babayanzad Ahari S. Pyridoxine (vitamin B6) therapy for premenstrual syndrome. Int J Gynaecol Obstet. 2007;96(1):43-4. doi: 10.1016/j.ijgo.2006.09.014.PubMedUsed to support: Randomized controlled trial in which pyridoxine reduced premenstrual syndrome symptoms. Adds controlled support for the PMS use.
  3. Kwan I, Onwude JL. Premenstrual syndrome. BMJ Clin Evid. 2007;2007:..PubMedUsed to support: Systematic review of premenstrual syndrome treatments that includes vitamin B6 among options with some supportive evidence. Context for the women's-health use.
  4. Vutyavanich T, Wongtra-ngan S, Ruangsri R. Pyridoxine for nausea and vomiting of pregnancy: a randomized, double-blind, placebo-controlled trial. Am J Obstet Gynecol. 1995;173(3 Pt 1):881-4. doi: 10.1016/0002-9378(95)90359-3.PubMedUsed to support: Randomized, double-blind, placebo-controlled trial in which pyridoxine reduced nausea and vomiting of pregnancy. Supports the morning-sickness use of B6.
  5. McParlin C, O'Donnell A, Robson SC, Beyer F, Moloney E, Bryant A, Bradley J, Muirhead CR, Nelson-Piercy C, Newbury-Birch D, Norman J, Shaw C, Simpson E, Swallow B, Yates L, Vale L. Treatments for Hyperemesis Gravidarum and Nausea and Vomiting in Pregnancy: A Systematic Review. JAMA. 2016;316(13):1392-1401. doi: 10.1001/jama.2016.14337.PubMedUsed to support: JAMA systematic review of treatments for nausea and vomiting in pregnancy; pyridoxine (vitamin B6) was among the options associated with greater benefit than placebo for mild symptoms, though the authors rated the overall quality of evidence as low. Supports the anti-nausea use of B6.
  6. Zhang Q, Ye X, Shi S, Zhou S, Ma D, Ouyang W, Tong J, Le Y. Pyridoxine Prevents Postoperative Nausea and Vomiting in Gynecologic Laparoscopic Surgery: A Double-blind Randomized Controlled Trial. Anesthesiology. 2025;142(4):655-665. doi: 10.1097/ALN.0000000000005354.PubMedUsed to support: Recent randomized controlled trial in which pyridoxine prevented postoperative nausea and vomiting. Extends B6's anti-nausea evidence.