NutriStack
Phenytoin and Vitamin B9, a caution.
Phenytoin depletes folate and folate supplementation may reduce phenytoin levels. This bidirectional interaction requires careful management.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Phenytoin and Vitamin B9
- Pair type
- Caution
- Evidence (highest tier)
- Strong
- Source citations
- 1 source
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Strong evidence
Caution
What is happening. Phenytoin depletes folate and folate supplementation may reduce phenytoin levels. This bidirectional interaction requires careful management.
Mechanism. Phenytoin inhibits intestinal folate absorption and increases folate catabolism. Conversely, folate enhances phenytoin metabolism by providing methyl groups for conjugation reactions.
Recommendation. Low-dose folate (400-1000mcg/day) is recommended on phenytoin. Avoid high-dose folate (>5mg) as it may reduce phenytoin levels. Monitor drug levels when adjusting folate.
Sources (1)
Stack Score
How this pair moves the number.
Effect on the composite score
If both Phenytoin and Vitamin B9 are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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