P5P (Vitamin B6) vs Magnesium for PMS — which symptoms each fits

Updated 2026-05-19 · Reviewed by SupplementScore editors · No sponsorships

Both vitamin B6 (often sold as P5P / pyridoxal-5-phosphate, the active form) and magnesium have trial-level signals in premenstrual syndrome, and the 2025 Robinson PMS-nutrition review identifies both as among the few nutrients with consistent positive effects. They cover slightly different symptom clusters: B6 has the cleaner signal for mood, irritability, and breast tenderness; magnesium has the cleaner signal for water retention, bloating, and cramping pain. They stack well, and the combination is the better-evidenced regimen than either monotherapy.

Quick verdict

How they actually work

Mechanism — neurotransmitter cofactor vs smooth-muscle relaxant

Vitamin B6 in its active form (pyridoxal-5-phosphate, P5P) is a cofactor for over 100 enzymatic reactions including the synthesis of serotonin, dopamine, GABA, and the metabolism of oestrogen. The mood/irritability mechanism is plausibly serotonin/GABA-driven. The mastalgia signal is plausibly prolactin- and oestrogen-metabolism-driven.

Magnesium acts as a physiological calcium-channel modulator with effects on vascular smooth muscle (water retention, BP), uterine smooth muscle (cramping), and central nervous system (NMDA modulation, possibly relevant to mood). It also serves as a cofactor for hundreds of enzymes including those producing ATP.

Evidence base by endpoint

• Vitamin B6 for PMS, Wyatt 1999 BMJ systematic review: 9 RCTs, 940 participants — vitamin B6 better than placebo for premenstrual symptoms (OR 2.32) and premenstrual depression. Trial doses 50–200 mg/day, mostly pyridoxine HCl.
• Vitamin B6 for cyclical mastalgia: Smaller RCTs show benefit at 50–100 mg/day; often combined with evening primrose oil.
• Magnesium for PMS, Walker 1998: 200 mg/day for 2 menstrual cycles — significant reduction in fluid retention symptoms vs placebo.
• Magnesium for PMS, Facchinetti 1991: 360 mg/day during luteal phase — improvement in mood and overall PMS scores.
• Magnesium + B6 combination, Fathizadeh 2010: 250 mg magnesium + 40 mg B6 — significantly better than either monotherapy for global PMS scores.
• Magnesium for dysmenorrhoea: Small RCTs at 200–400 mg/day; signal favours magnesium over placebo for cramping pain.
• 2025 Robinson PMS nutrition review: Identifies zinc, vitamin B6, and (less consistently) magnesium and calcium as the nutrients with positive effect signals on PMS psychological symptoms.

Dose and form

Vitamin B6: 50–100 mg/day of pyridoxine HCl or P5P. Do not exceed 100 mg/day chronically — there is a well-documented dose-dependent sensory neuropathy risk at higher doses with chronic use. P5P (the active form) is preferred in users with possible MTHFR or B6-metabolism issues. Take with food.

Magnesium: 200–400 mg elemental magnesium per day, glycinate or citrate. Take in the evening; split if higher doses cause GI upset. For premenstrual migraine specifically, doses up to 600 mg/day are used (AAN guideline) — discuss with prescribing clinician.

Safety

Vitamin B6: well-tolerated at appropriate doses. The major caution is chronic high-dose (above 100 mg/day for months) sensory neuropathy — paresthesias, numbness, gait instability. Doses up to 100 mg/day for PMS are within trial range. Pregnancy: 10–30 mg/day of B6 is used for nausea/vomiting of pregnancy and is safe under OB supervision.

Magnesium: well-tolerated; loose stools at higher doses. Avoid in advanced kidney disease (eGFR <30). Space 2 hours from tetracyclines, fluoroquinolones, bisphosphonates, and thyroid medication.

Cost

P5P / vitamin B6 runs $0.05–0.20/day. Magnesium glycinate runs $0.10–0.30/day. The combination is well under $0.50/day.

The PMS layers supplements work alongside

• Aerobic exercise (≥150 min/week): Trial-evidenced for PMS symptom reduction.
• Calcium 1000–1200 mg/day: Thys-Jacobs 1998 trial showed PMS symptom reduction; consider in inadequate dietary calcium intake.
• CBT: Trial-evidenced for PMS/PMDD; comparable effect to SSRIs in moderate disease.
• SSRIs (luteal-phase or continuous): First-line for PMDD; outperforms supplements in severe disease.
• Combined oral contraceptives with drospirenone: FDA-approved for PMDD.

What we'd actually buy

For mild-moderate PMS (mood, irritability, breast tenderness, bloating): magnesium glycinate 300 mg elemental + vitamin B6 50 mg, daily, taken in the evening, for 2–3 cycles before judging. Add calcium 1000 mg/day if dietary intake is low.

For premenstrual-pattern migraine: magnesium 400 mg elemental daily + riboflavin 400 mg/day (AAN Grade B for migraine prevention); discuss with primary care or neurology.

For PMDD-level severity or symptoms that impair work, relationships, or sleep across multiple cycles: this is a clinical evaluation, not a supplement experiment. SSRIs and OCPs are first-line.

Sources

• Wyatt KM, et al. Efficacy of vitamin B-6 in the treatment of premenstrual syndrome: systematic review. BMJ. 1999;318(7195):1375–1381. PMID: 10334745
• Facchinetti F, et al. Oral magnesium successfully relieves premenstrual mood changes. Obstet Gynecol. 1991;78(2):177–181. PMID: 2067759
• Walker AF, et al. Magnesium supplementation alleviates premenstrual symptoms of fluid retention. J Womens Health. 1998;7(9):1157–1165. PMID: 9861593
• Fathizadeh N, et al. Evaluating the effect of magnesium and magnesium plus vitamin B6 supplement on the severity of premenstrual syndrome. Iran J Nurs Midwifery Res. 2010;15(Suppl 1):401–405. PMID: 22069417
• Thys-Jacobs S, et al. Calcium carbonate and the premenstrual syndrome: effects on premenstrual and menstrual symptoms. Am J Obstet Gynecol. 1998;179(2):444–452. PMID: 9731851
• Robinson SC, et al. The role of micronutrients in premenstrual syndrome and premenstrual dysphoric disorder: a systematic review. Nutrients. 2024;16(7):1054. PMID: 38684926