The short answer
Have high-dose vitamin B6 reviewed before using it with phenobarbital. NIH describes lower phenobarbital levels with high-dose pyridoxine, but the effect of lower doses is unknown.
What this answer covers
Evidence concerns supplemental pyridoxine, particularly 200 mg/day exposures; not all B6 vitamers, foods or ordinary nutritional intake.
- Supplement or preparation
- Vitamin B6
- Medication ingredient
- phenobarbital
The dose and form matter
The cited research summarized by NIH used pyridoxine at 200 mg a day. That is a high supplemental exposure. Whether lower doses affect phenobarbital levels is unknown; the evidence should not be applied equally to every B6 form.
Review overlapping products
Bring B-complex products, multivitamins and any separate B6 supplement. Excess B6 can itself cause neurological problems, and your clinician needs the total amount when assessing new symptoms.
Do not rely on a timing gap
The reported concern is lower medicine concentrations, possibly from altered metabolism. No validated interval shows that spacing B6 and phenobarbital prevents it. Ask whether drug-level or symptom monitoring is appropriate.
Keep the prescribed medicine steady
Do not stop phenobarbital abruptly or adjust its dose to compensate for a supplement. Sudden withdrawal can provoke serious seizures. Tell the prescriber about new or worsening symptoms and all supplement changes.
Evidence and practical considerations
Absorption & effectiveness
Conditional high-dose review is supported by the official nutrient assessment; no universal B6 avoidance or dose-separation rule.
- Exact scope
- Evidence concerns supplemental pyridoxine, particularly 200 mg/day exposures; not all B6 vitamers, foods or ordinary nutritional intake. with Exact oral phenobarbital; parent and metabolites distinguished; no other drug/route assumed equivalent.
- Medication form and route
- oral supplement unless pregnancy section explicitly distinguishes neonatal injection
- Timing or duration
- Preparation, dose and duration determine applicability; chronic nutrition evidence is not a single-dose interaction.
What remains uncertain
- Original 1976 letter is bibliographic-only in this capture; details rely on NIH assessment. No proven lower-dose threshold or clinical seizure-effect magnitude.
Factors that may matter: exact supplement identity; dose; other medicines; clinical indication; baseline nutrition; pregnancy where relevant.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed oral phenobarbital.
Causes CNS depression and can impair driving; other CNS depressants can add to these effects. Adult plasma half-life is prolonged. Abrupt withdrawal after dependence can cause seizures and other serious symptoms. Long-term treatment warrants periodic clinical and laboratory assessment.
How this applies: Exact RxCUI 8134 IN and UNII YQE403BP4D, oral plain ingredient; no automatic sodium-injection or other barbiturate transfer.
Does not name the requested botanicals or establish supplement-specific interaction rates or spacing. Current DailyMed listing is unapproved drug other, not evidence of FDA approval.
Source 2: official nutrient guidance
ods.od.nih.gov · Source check Sep 10, 2026
Population: People using vitamin B6 and antiseizure medicines.
Reports that these high-dose pyridoxine exposures can lower phenobarbital concentrations; effects of lower doses are unknown. Excess supplemental B6 can cause neurological toxicity.
How this applies: Exact named phenobarbital and pyridoxine context supports high-dose review, not a universal avoidance or spacing rule.
1976 original letter has no accessible abstract in captured MED record; original full text not obtained. Dose information is from this official assessment, not independently reconstructed. Does not establish all B6 vitamers or meal-level exposure effects.
Source 3: original clinical research
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: Original letter indexed for epilepsy and phenobarbital/phenytoin concentrations.
Bibliographic record confirms the original report exists; no abstract or original numeric results are available in this capture.
How this applies: Apply only to the named drugs and study exposures; no unmeasured parent/metabolite or preparation equivalence.
Bibliographic only, not independent clinical outcome support. Official NIH assessment is the accessible source for the described high-dose finding.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Exact current available claims reviewed against captured originals; no clinical review asserted. | |
| Research summary published |
Article revision: 3a8f183490343f7b
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.