NutriStack
Carbamazepine and Phenytoin, a caution.
Both are potent CYP enzyme inducers that affect each other's metabolism. Phenytoin can decrease carbamazepine levels, while carbamazepine can decrease phenytoin levels, making dose optimization challenging.
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
- Carbamazepine and Phenytoin
- 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. Both are potent CYP enzyme inducers that affect each other's metabolism. Phenytoin can decrease carbamazepine levels, while carbamazepine can decrease phenytoin levels, making dose optimization challenging.
Mechanism. Both drugs are CYP3A4 inducers and CYP3A4 substrates. Mutual induction of hepatic metabolism leads to reduced plasma levels of both drugs, requiring higher doses to maintain therapeutic levels.
Recommendation. Monitor serum levels of both drugs closely when used together. Dose adjustments are frequently needed. Therapeutic drug monitoring is essential.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Carbamazepine and Phenytoin 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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