What the FDA labels say about taking them together
Granisetron and phenobarbital
Granisetron's FDA label of August 31, 2017 names phenobarbital in its drug interactions section; the phenobarbital labels PlainMeds reads (2) do not name granisetron. The granisetron label: “In a human pharmacokinetic study, hepatic enzyme induction with phenobarbital resulted in a 25% increase in total plasma clearance of intravenous granisetron hydrochloride.”
Check it at the source: the granisetron FDA label on DailyMed (effective August 31, 2017, Mylan Institutional LLC); the phenobarbital FDA label on DailyMed (effective August 27, 2026).
What does the granisetron label say about phenobarbital?
Granisetron label, drug interactionsIn a human pharmacokinetic study, hepatic enzyme induction with phenobarbital resulted in a 25% increase in total plasma clearance of intravenous granisetron hydrochloride.
Source: FDA drug label (Granisetron Hydrochloride), Mylan Institutional LLC, effective August 31, 2017 (SPL set 8d88adba-7f5e-4e97-84b3-6ca8ec98c023), via openFDA; the full label on DailyMed
What does the phenobarbital label say about granisetron?
Phenobarbital's label (effective August 27, 2026) and its 1 other brand-application label do not name granisetron 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
| Granisetron | Phenobarbital | |
|---|---|---|
| Labeled for | Nausea and vomiting | Seizures and epilepsy |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $1.31 per tablet 1 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