Vitamin B6 (pyridoxine)
ACOG first-line pharmacotherapy for nausea and vomiting of pregnancy. Also evidenced for premenstrual symptom relief at up to 100 mg/day.
Why
Pyridoxine is the rare vitamin with a guideline-endorsed therapeutic role: ACOG Practice Bulletin 189 (2018) recommends pyridoxine 10–25 mg orally three to four times daily, alone or combined with doxylamine, as first-line pharmacotherapy for nausea and vomiting of pregnancy. Outside pregnancy, the Wyatt 1999 BMJ systematic review (9 trials, n=940) found doses up to 100 mg/day improved overall premenstrual symptoms (OR 2.32) and premenstrual depression (OR 1.69), though the authors flagged the included trials as low-quality.
How it works
Pyridoxal-5-phosphate (PLP) is a cofactor for >100 enzymes including those in neurotransmitter synthesis (serotonin, GABA, dopamine), haem synthesis, and homocysteine metabolism via cystathionine-β-synthase.
Expected onset · Nausea relief often within 1–3 days; PMS improvement over 1–2 menstrual cycles
How to take
Dosage
Morning sickness: 10–25 mg three to four times daily (ACOG 2018). PMS: up to 100 mg/day (Wyatt 1999 systematic review). Do not exceed 100 mg/day long-term outside medical supervision, higher chronic intakes risk sensory neuropathy.
Timing
Divided doses with meals; in pregnancy often dosed against the worst-symptom window
On the label
Pyridoxine HCl is the form used in the ACOG and Wyatt evidence base. P-5-P (pyridoxal-5-phosphate) is the active form but carries no proven advantage at standard doses.
Ideal for
Pregnant people with morning sickness; people with premenstrual symptoms unresponsive to lifestyle measures; people on isoniazid, hydralazine, or penicillamine (drugs that deplete B6).
Safety
Evidence
ACOG Practice Bulletin 189 (2018) names pyridoxine 10–25 mg orally 3–4×/day, alone or with doxylamine, as first-line pharmacotherapy for nausea and vomiting of pregnancy. Wyatt 1999 BMJ systematic review (9 trials, n=940) for PMS: doses up to 100 mg/day improved overall symptoms (OR 2.32, 95% CI 1.95–2.54).
- Wyatt et al., BMJ 1999, systematic review (9 trials, n=940) of vitamin B6 up to 100 mg/day for premenstrual syndrome
- Matthews et al., Cochrane Database Syst Rev 2015, interventions for nausea and vomiting in early pregnancy (41 trials, n=5,449)
- ACOG Practice Bulletin 189, 2018, pyridoxine 10–25 mg 3–4×/day as first-line for NVP
Where to get it
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