What the FDA labels say about taking them together
Phenytoin and risperidone
Risperidone's FDA label (Risperdal Consta) of November 5, 2025 names phenytoin in its drug interactions section; the phenytoin labels PlainMeds reads (2) do not name risperidone. The risperidone label: “Co-administration of other known CYP 3A4 enzyme inducers with risperidone may cause similar decreases in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone, which could lead to decreased efficacy …”
Check it at the source: the phenytoin FDA label on DailyMed (effective October 15, 2024, Mylan Pharmaceuticals Inc.); the risperidone FDA label on DailyMed (effective May 28, 2026, Janssen Pharmaceuticals, Inc.).
What does the phenytoin label say about risperidone?
Phenytoin's label (effective October 15, 2024) and its 1 other brand-application label do not name risperidone in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Phenytek), Mylan Pharmaceuticals Inc., effective October 15, 2024 (SPL set 0f94c791-8b07-4b41-927e-c9f28bec5f60), via openFDA; the full label on DailyMed
What does the risperidone label say about phenytoin?
Risperdal Consta label (Janssen Pharmaceuticals, Inc., November 5, 2025), drug interactionsCo-administration of other known CYP 3A4 enzyme inducers (e.g., phenytoin, rifampin, and phenobarbital) with risperidone may cause similar decreases in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone, which could lead to decreased efficacy of RISPERDAL CONSTA treatment.
Source: FDA drug label (Risperdal Consta, NDA021346), Janssen Pharmaceuticals, Inc., effective November 5, 2025 (SPL set bb34ee82-d2c2-43b8-ba21-2825c0954691), via openFDA
Source: FDA drug label (RISPERDAL), Janssen Pharmaceuticals, Inc., effective May 28, 2026 (SPL set 7e117c7e-02fc-4343-92a1-230061dfc5e0), 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
| Phenytoin | Risperidone | |
|---|---|---|
| Labeled for | Seizures and epilepsy | Bipolar disorder, Schizophrenia |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per capsule 100 mg capsule | $0.0368 per tablet 0.25 mg tablet |
| Shortage now | No current entry | 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