Fluvoxamine and Thioridazine interaction
Fluvoxamine and Thioridazine: 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 Fluvoxamine (fluvoxamine maleate) label · effective 2026-04-23
Coadministration Coadministration of tizanidine, thioridazine, alosetron, or pimozide with Fluvoxamine Maleate Tablets is contraindicated [see Warnings and Precautions ( 5.4 , 5.5 , 5.6 , 5.7 )] .
Coadministration of tizanidine, thioridazine, alosteron, pimozide ( 4 )
Thioridazine administration produces a dose-related prolongation of the QTc interval, which is associated with serious ventricular arrhythmias, such as torsades de pointes-type arrhythmias, and sudden death.
Therefore, fluvoxamine and thioridazine should not be coadministered [see Contraindications ( 4 )] .
Concentrations of thioridazine and its two active metabolites, mesoridazine and sulforidazine, increased threefold following coadministration of fluvoxamine.
From the Thioridazine (Thioridazine Hydrochloride) label · effective 2026-03-02
Reduced cytochrome P450 2D6 isozyme activity drugs that inhibit this isozyme (e.g., fluoxetine and paroxetine) and certain other drugs (e.g., fluvoxamine, propranolol, and pindolol) appear to appreciably inhibit the metabolism of thioridazine.
Fluvoxamine and thioridazine should not be coadministered.
Drug Interactions Reduced cytochrome P450 2D6 isozyme activity, drugs which inhibit this isozyme (e.g., fluoxetine and paroxetine), and certain other drugs (e.g., fluvoxamine, propranolol, and pindolol) appear to appreciably inhibit the metabolism of thioridazine.
Drugs That Reduce the Clearance of Thioridazine Through Other Mechanisms Fluvoxamine The effect of fluvoxamine (25 mg b.i.d. for one week) on thioridazine steady-state concentration was evaluated in ten male inpatients with schizophrenia.
Concentrations of thioridazine and its two active metabolites, mesoridazine and sulforidazine, increased 3-fold following coadministration of fluvoxamine.
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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.