What the FDA labels say about taking them together
Glycerol phenylbutyrate and haloperidol
Glycerol phenylbutyrate's FDA label of October 29, 2025 names haloperidol in its drug interactions section; the haloperidol labels PlainMeds reads (2) do not name glycerol phenylbutyrate. The glycerol phenylbutyrate label: “DRUG INTERACTIONS Corticosteroids, valproic acid, or haloperidol: May increase plasma ammonia level; monitor ammonia levels closely.”
Check it at the source: the glycerol phenylbutyrate FDA label on DailyMed (effective October 29, 2025, Horizon Therapeutics USA, Inc.); the haloperidol FDA label on DailyMed (effective April 23, 2026, PD-Rx Pharmaceuticals, Inc.).
What does the glycerol phenylbutyrate label say about haloperidol?
Glycerol phenylbutyrate label, drug interactionsDRUG INTERACTIONS Corticosteroids, valproic acid, or haloperidol: May increase plasma ammonia level; monitor ammonia levels closely.
Source: FDA drug label (Ravicti), Horizon Therapeutics USA, Inc., effective October 29, 2025 (SPL set 900e7dc0-9afe-4f50-80de-90567bb78519), via openFDA; the full label on DailyMed
What does the haloperidol label say about glycerol phenylbutyrate?
Haloperidol's label (effective April 23, 2026) and its 1 other brand-application label do not name glycerol phenylbutyrate in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Haloperidol), PD-Rx Pharmaceuticals, Inc., effective April 23, 2026 (SPL set 533b0b4c-cbd6-4ec0-a333-8b04b5b43a1d), 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
| Glycerol phenylbutyrate | Haloperidol | |
|---|---|---|
| Labeled for | n/a | Schizophrenia |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | n/a | $15.60 per mL 100 mg/mL vial |
| Shortage now | A presentation being discontinued | 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