Phenytoin and Risperidone interaction
Phenytoin and Risperidone: the Risperidone prescribing label describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Risperidone (RISPERDAL CONSTA) label · effective 2025-11-05
Carbamazepine and other enzyme inducers decrease plasma concentrations of risperidone.
Carbamazepine and Other CYP 3A4 Enzyme Inducers Carbamazepine co-administration with oral RISPERDAL decreased the steady-state plasma concentrations of risperidone and 9-hydroxyrisperidone by about 50%.
Co-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.
At the initiation of therapy with carbamazepine or other known hepatic enzyme inducers, patients should be closely monitored during the first 4–8 weeks, since the dose of RISPERDAL CONSTA may need to be adjusted.
On discontinuation of carbamazepine or other CYP 3A4 hepatic enzyme inducers, the dosage of RISPERDAL CONSTA should be re-evaluated and, if necessary, decreased.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.