What the FDA labels say about taking them together
Clonazepam and phenobarbital
Clonazepam's FDA label of December 1, 2025 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name clonazepam. The clonazepam label: “Cytochrome P-450 inducers, such as phenytoin, carbamazepine, lamotrigine, and phenobarbital induce clonazepam metabolism, causing an approximately 38% decrease in plasma clonazepam levels.”
Check it at the source: the clonazepam FDA label on DailyMed (effective December 1, 2025, H2-Pharma, LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the clonazepam label say about phenobarbital?
Clonazepam label, drug interactionsCytochrome P-450 inducers, such as phenytoin, carbamazepine, lamotrigine, and phenobarbital induce clonazepam metabolism, causing an approximately 38% decrease in plasma clonazepam levels.
Source: FDA drug label (Klonopin), NDA017533 (Cheplapharm), as published by H2-Pharma, LLC, effective December 1, 2025 (SPL set cfa0d79a-843c-4b88-95a1-e9511d649ca1), via openFDA; the full label on DailyMed
What does the phenobarbital label say about clonazepam?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name clonazepam 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
| Clonazepam | Phenobarbital | |
|---|---|---|
| Labeled for | Seizures and epilepsy, Anxiety | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0244 per tablet 1 mg tablet | $0.213 per tablet 100 mg tablet |
| Shortage now | In shortage | 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