Fluoxetine and Thioridazine interaction
Fluoxetine 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 Fluoxetine (Prozac) label · effective 2026-01-08
Risk of QT prolongation and drug interaction ( 4.2 , 5.11 , 7.7 , 7.8 ) Thioridazine: Do not use.
Risk of QT interval prolongation and elevated thioridazine plasma levels.
Do not use thioridazine within 5 weeks of discontinuing PROZAC.
Do not use thioridazine within 5 weeks of discontinuing PROZAC ( 4.2 , 5.11 , 7.7 , 7.8 ) When using PROZAC and olanzapine in combination, also refer to the Contraindications section of the package insert for Symbyax ( 4 )
Other Contraindications The use of PROZAC is contraindicated with the following: Pimozide [see Warnings and Precautions ( 5.11 ) and Drug Interactions ( 7.7 , 7.8 )] Thioridazine [see Warnings and Precautions ( 5.11 ) and Drug Interactions ( 7.7 , 7.8 )] Pimozide and thioridazine prolong the QT interval.
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.
CONTRAINDICATIONS Thioridazine hydrochloride tablet use should be avoided in combination with other drugs that are known to prolong the QTc interval and in patients with congenital long QT syndrome or a history of cardiac arrhythmias.
Such an increased risk may result also from the additive effect of coadministering thioridazine with other agents that prolong the QTc interval.
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.
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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.