Lamotrigine and Phenobarbital Interaction
Drug interaction information between Lamotrigine and Phenobarbital.
Lamotrigine and Phenobarbital have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Lamotrigine and Phenobarbital. 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
Phenobarbital makes your body get rid of lamotrigine more quickly, which can lower the medicine's levels in your blood by about 40%.
FDA Label Information
Phenobarbital/Primidone ↓ 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
Phenobarbital Also Interacts With
- Nirmatrelvir/Ritonavir major
- Ranolazine major
- Voriconazole major
- Canagliflozin moderate
- Cenobamate moderate
Frequently Asked Questions
What SPL severity band is on file for Lamotrigine + Phenobarbital?
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?
Phenobarbital has 59 labeled pairs on file vs Lamotrigine's 24. In the minor band specifically: Lamotrigine has 22 (also Valproate, Carbamazepine, Rifampin, Phenytoin); Phenobarbital has 43 (also Estradiol, Doxycycline, Progesterone, Griseofulvin).
What mechanism field is on file for Lamotrigine and Phenobarbital?
Phenobarbital makes your body get rid of lamotrigine more quickly, which can lower the medicine's levels in your blood by about 40%.
Phenobarbital carries more major-labeled pairs than Lamotrigine
SPL source-record counts only. This page's band is minor · classes on file: Lamotrigine (Anticonvulsant); Phenobarbital (Anticonvulsant (Barbiturate)).
Phenobarbital has 3 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
- Phenytoin
3 major · 13 moderate · 43 minor · 59 total
- Other minor peers for Phenobarbital
- Estradiol
- Doxycycline
- Progesterone
- Griseofulvin
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.