What the FDA labels say about taking them together
Lenacapavir and phenobarbital
Lenacapavir's FDA label of August 27, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name lenacapavir. The lenacapavir label: “Concomitant administration of carbamazepine, oxcarbazepine, phenobarbital, or phenytoin may result in loss of therapeutic effect and development of resistance. …”
Check it at the source: the lenacapavir FDA label on DailyMed (effective August 27, 2026, Gilead Sciences, Inc.); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the lenacapavir label say about phenobarbital?
Lenacapavir label, drug interactionsConcomitant Drug Class/Drug Name: Anticonvulsants: carbamazepine oxcarbazepine phenobarbital phenytoin; Effect on Concentration ↑ = Increase, ↓ = Decrease.: ↓ lenacapavir; Clinical Comment: Concomitant administration of carbamazepine, oxcarbazepine, phenobarbital, or phenytoin may result in loss of therapeutic effect and development of resistance. Concomitant administration of SUNLENCA with carbamazepine or phenytoin is contraindicated. Concomitant administration of SUNLENCA with oxcarbazepine or phenobarbital is not recommended. Consider use of alternative anticonvulsants.
Source: FDA drug label (Sunlenca), Gilead Sciences, Inc., effective August 27, 2026 (SPL set e5652804-29c4-40d7-aeb2-0142ed2a7b5b), via openFDA; the full label on DailyMed
What does the phenobarbital label say about lenacapavir?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name lenacapavir in these sections. A label lists what its studies and reports found; it is not a complete list.
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
| Lenacapavir | Phenobarbital | |
|---|---|---|
| Labeled for | HIV | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | n/a | $0.213 per tablet 100 mg tablet |
| Shortage now | No current entry | 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