What the FDA labels say about taking them together
Phenobarbital and tadalafil
Tadalafil's FDA label of June 3, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name tadalafil. The tadalafil label: “Although specific interactions have not been studied, other CYP3A4 inducers, such as carbamazepine, phenytoin, and phenobarbital, would likely decrease tadalafil exposure.”
Check it at the source: the phenobarbital FDA label on DailyMed (effective August 27, 2026); the tadalafil FDA label on DailyMed (effective June 3, 2026, Eli Lilly and Company).
What does the phenobarbital label say about tadalafil?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name tadalafil 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
What does the tadalafil label say about phenobarbital?
Tadalafil label, drug interactionsAlthough specific interactions have not been studied, other CYP3A4 inducers, such as carbamazepine, phenytoin, and phenobarbital, would likely decrease tadalafil exposure.
Source: FDA drug label (Cialis), Eli Lilly and Company, effective June 3, 2026 (SPL set bcd8f8ab-81a2-4891-83db-24a0b0e25895), 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
| Phenobarbital | Tadalafil | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Erectile dysfunction, Enlarged prostate (BPH), Pulmonary arterial hypertension |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.213 per tablet 100 mg tablet | $0.167 per tablet 20 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