What is the appropriate dose of vitamin B6 (pyridoxine) for an otherwise healthy adult with mild-to-moderate nausea (e.g., morning‑sickness‑type)?

Vitamin B6 Dosing for Nausea in Otherwise Healthy Adults

For mild-to-moderate nausea in an otherwise healthy adult, start with pyridoxine 10–20 mg taken 2–4 times daily (total 20–40 mg/day), which is the evidence-based dose used in pregnancy-related nausea and remains far below toxicity thresholds. 1

Recommended Dosing Algorithm

Initial therapy:

• Start with 10 mg pyridoxine at bedtime on Day 1 1
• If nausea persists, escalate to 10 mg twice daily (morning and bedtime) 1
• Maximum effective dose is 40 mg total per day (10 mg four times daily) 1

This dosing is derived from the American College of Obstetricians and Gynecologists' first-line regimen for nausea and vomiting of pregnancy, where pyridoxine is combined with doxylamine (the combination product contains 10 mg pyridoxine per tablet, with up to 4 tablets daily recommended). 1 While the guideline addresses pregnancy, the pyridoxine component's anti-nausea mechanism is not pregnancy-specific and applies to general nausea management.

Safety Considerations

The 20–40 mg/day range is extremely safe:

• This dose is 50–100 times lower than the threshold where toxicity begins to appear (100–300 mg/day chronically) 2, 3
• The U.S. safe upper limit is set at 100 mg/day, with no-observed-adverse-effect-level at 200 mg/day 2
• Long-term studies using 100–150 mg/day in adults showed minimal or no toxicity over 5–10 years 3

Toxicity only occurs with:

• Chronic daily intake exceeding 100–300 mg 1, 2
• Doses of 1000 mg/day or higher (800 times normal dietary intake) 2
• Manifestations include sensory neuropathy, ataxia, and areflexia 4

Clinical Context and Mechanism

Pyridoxine (vitamin B6) functions as a cofactor in neurotransmitter synthesis, including serotonin production, which may explain its anti-nausea effects. 3 The vitamin is water-soluble with no significant body stores, making daily intake necessary for therapeutic effect. 5

Important Caveats

When this regimen fails to control nausea:

• Consider escalating to antiemetics like metoclopramide or ondansetron 1
• Evaluate for underlying causes requiring specific treatment
• Consider IV hydration if severe symptoms with dehydration develop 1

Do not confuse anti-nausea dosing with other B6 indications:

• Isoniazid neuropathy prophylaxis uses 25–100 mg/day 1, 4
• Vincristine-induced neuropathy treatment uses 100–200 mg/day 4
• These higher doses serve different therapeutic purposes