What the FDA labels say about taking them together
Diazepam and phenobarbital
Diazepam's FDA label (Valtoco) of June 3, 2026 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name diazepam. The diazepam label: “Inducers of CYP2C19 and CYP3A4 Inducers of CYP2C19 (e.g., rifampin) and CYP3A4 could increase the rate of diazepam elimination; therefore, efficacy of VALTOCO may be decreased.”
Check it at the source: the diazepam FDA label on DailyMed (effective August 11, 2026, Waylis Therapuetics LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the diazepam label say about phenobarbital?
Valtoco label (Neurelis, Inc, June 3, 2026), drug interactionsInducers of CYP2C19 and CYP3A4 Inducers of CYP2C19 (e.g., rifampin) and CYP3A4 (e.g., carbamazepine, phenytoin, dexamethasone, and phenobarbital) could increase the rate of diazepam elimination; therefore, efficacy of VALTOCO may be decreased.
Source: FDA drug label (Valtoco, NDA211635), Neurelis, Inc, effective June 3, 2026 (SPL set 1a8bcc90-68fa-474d-832c-0df01e825f39), via openFDA
Source: FDA drug label (Valium), Waylis Therapuetics LLC, effective August 11, 2026 (SPL set 260e2041-2bb3-482f-850e-b5d47a7bdbe6), via openFDA; the full label on DailyMed
What does the phenobarbital label say about diazepam?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name diazepam 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
| Diazepam | Phenobarbital | |
|---|---|---|
| Labeled for | Anxiety, Muscle spasms and spasticity | Seizures and epilepsy |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.0283 per tablet 10 mg tablet | $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