What the FDA labels say about taking them together
Lamotrigine and phenobarbital
Lamotrigine's FDA label of October 10, 2025 names phenobarbital in its drug interactions section; phenobarbital's label does not name lamotrigine itself but warns about its class (Anti-seizure medicines). The lamotrigine label: “Decreased lamotrigine concentration approximately 40%.”
Check it at the source: the lamotrigine FDA label on DailyMed (effective October 10, 2025); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the lamotrigine label say about phenobarbital?
Lamotrigine label, drug interactionsConcomitant Drug: Phenobarbital/primidone; Effect on Concentration of Lamotrigine or Concomitant Drug: ↓ lamotrigine; Clinical Comment: Decreased lamotrigine concentration approximately 40%.
Subvenite label (OWP Pharmaceuticals, Inc., June 4, 2026), drug interactionsDRUG INTERACTIONS Valproate increases lamotrigine concentrations more than 2-fold. ( 7 , 12.3 ) Carbamazepine, phenytoin, phenobarbital, primidone, and rifampin decrease lamotrigine concentrations by approximately 40%. ( 7 , 12.3 ) Estrogen-containing oral contraceptives decrease lamotrigine concentrations by approximately 50%. ( 7 , 12.3 ) Protease inhibitors lopinavir/ritonavir and atazanavir/lopinavir decrease lamotrigine exposure by approximately 50% and 32%, respectively. ( 7 , 12.3 ) Coadministration with organic cationic transporter 2 substrates with narrow therapeutic index is not recommended ( 7 , 12.3 ) Significant drug interactions with SUBVENITE are summarized in this section.
Source: FDA drug label (Subvenite, NDA218879), OWP Pharmaceuticals, Inc., effective June 4, 2026 (SPL set 022b0913-f683-4af8-a862-f81b315909b2), via openFDA
Source: FDA drug label (LAMICTAL), GlaxoSmithKline LLC, effective October 10, 2025 (SPL set d7e3572d-56fe-4727-2bb4-013ccca22678), via openFDA; the full label on DailyMed
What does the phenobarbital label say about lamotrigine?
Phenobarbital's label does not name lamotrigine itself; it warns about its class (Anti-seizure medicines):
Phenobarbital label, warnings and precautionsIf a rash occurs, the patient should be evaluated for signs and symptoms of Drug Reaction with Eosinophilia and Systemic Symptoms [see Warnings and Precautions (5.6)]. Reaction with Eosinophilia and Systemic Symptoms (DRESS)/Multiorgan Hypersensitivity Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS), also known as multiorgan hypersensitivity, has been reported in patients taking antiepileptic drugs, including phenobarbital.
Phenobarbital label, warnings and precautionsAntiepileptic drugs (AEDs) increase the risk of suicidal thoughts or behavior in adolescents and adults.
Source: FDA drug label (Phenobarbital), Chartwell RX, LLC, effective August 27, 2026 (SPL set 74428144-fb24-40a5-a670-3b876e2d116c), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Lamotrigine | Phenobarbital | |
|---|---|---|
| Labeled for | Seizures and epilepsy, Bipolar disorder | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0268 per tablet 25 mg tablet | $0.213 per tablet 100 mg tablet |
| Shortage now | A presentation being discontinued | A presentation being discontinued |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once