Lamotrigine and Phenytoin Interaction
Drug interaction information between Lamotrigine and Phenytoin.
Lamotrigine and Phenytoin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Lamotrigine and Phenytoin. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
How They Interact
Phenytoin speeds up the way your body processes lamotrigine, which reduces the amount of medicine in your blood by about 40%.
FDA Label Information
Phenytoin ↓ lamotrigine Decreased lamotrigine concentration approximately 40%. ( 7 , 12.3 ) Carbamazepine, phenytoin, phenobarbital, primidone, and rifampin decrease lamotrigine concentrations by approximately 40%.
Lamotrigine Also Interacts With
- Dofetilide moderate
- Desmopressin moderate
- Valproate minor
- Carbamazepine minor
- Rifampin minor
Phenytoin Also Interacts With
- Nirmatrelvir/Ritonavir major
- Posaconazole major
- Ranolazine major
- Voriconazole major
- Apixaban moderate
Frequently Asked Questions
What SPL severity band is on file for Lamotrigine + Phenytoin?
Compiled FDA labeling labels this pair minor. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Phenytoin has 147 labeled pairs on file vs Lamotrigine's 24. In the minor band specifically: Lamotrigine has 22 (also Valproate, Carbamazepine, Rifampin, Phenobarbital); Phenytoin has 120 (also Atorvastatin, Omeprazole, Simvastatin, Methylphenidate).
What mechanism field is on file for Lamotrigine and Phenytoin?
Phenytoin speeds up the way your body processes lamotrigine, which reduces the amount of medicine in your blood by about 40%.
Phenytoin carries more major-labeled pairs than Lamotrigine
SPL source-record counts only. This page's band is minor · classes on file: Lamotrigine (Anticonvulsant); Phenytoin (Anticonvulsant (Hydantoin)).
Phenytoin has 4 major-labeled pairs vs Lamotrigine's 0. This page itself is in the minor band, not the major band.
0 major · 2 moderate · 22 minor · 24 total
- Other minor peers for Lamotrigine
- Valproate
- Carbamazepine
- Rifampin
- Phenobarbital
4 major · 23 moderate · 120 minor · 147 total
- Other minor peers for Phenytoin
- Atorvastatin
- Omeprazole
- Simvastatin
- Methylphenidate
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.