What the FDA labels say about taking them together
Lamotrigine and primidone
Lamotrigine's FDA label of October 10, 2025 names primidone in its drug interactions section; primidone'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 primidone FDA label on DailyMed (effective September 10, 2026, Bausch Health US, LLC).
What does the lamotrigine label say about primidone?
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 primidone label say about lamotrigine?
Primidone's label does not name lamotrigine itself; it warns about its class (Anti-seizure medicines):
Primidone label, warningsSuicidal Behavior and Ideation Antiepileptic drugs (AEDs), including MYSOLINE, increase the risk of suicidal thoughts or behavior in patients taking these drugs for any indication.
Primidone label, warningsPatients treated with any AED for any indication should be monitored for the emergence or worsening of depression, suicidal thoughts or behavior, and/or any unusual changes in mood or behavior.
Source: FDA drug label (Mysoline), NDA009170 (Valeant), as published by Bausch Health US, LLC, effective September 10, 2026 (SPL set af593171-dabb-4ea3-b44c-89ed457b2c46), 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 | Primidone | |
|---|---|---|
| Labeled for | Seizures and epilepsy, Bipolar disorder | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0268 per tablet 25 mg tablet | $0.0914 per tablet 50 mg tablet |
| Shortage now | A presentation being discontinued | No current entry |
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