Phenobarbital and Risperidone interaction
Phenobarbital and Risperidone: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Phenobarbital (SEZABY) label · effective 2025-12-23
CNS depressants: Closely monitor for sedation and respiratory depression.
Drugs that Prolong the QT Interval : Avoid concomitant use.
CNS Depressants Closely monitor for signs of sedation and respiratory depression with concomitant use of SEZABY with other CNS depressants, including opioids [see Warnings and Precautions (5.1)] .
QT Prolongation SEZABY may prolong the QT interval [see Clinical Pharmacology (12.2)] .
Drugs that Prolong QT Interval SEZABY may prolong the QT interval [see Warnings and Precautions (5.10) and Clinical Pharmacology (12.2)] .
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.
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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.