Olanzapine and fluoxetine and Thioridazine interaction
Olanzapine and 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 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.
…proarrhythmic effects, thioridazine should be reserved for use in the treatment of schizophrenic patients who fail to show an acceptable response to adequate courses of treatment with other antipsychotic drugs, either because of insufficient effectiveness or the inability to achieve an effective dose due to intolerable adverse effects from those drugs (see WARNINGS , CONTRAINDICATIONS…
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.
From the Olanzapine and fluoxetine label · effective 2026-03-31
Risk of QT interval prolongation ( 4.2 , 5.20 , 7.7 , 7.8 ) Thioridazine : Do not use.
Do not use thioridazine within 5 weeks of discontinuing olanzapine and fluoxetine capsules ( 4.2 , 5.20 , 7.7 , 7.8 ) 4.1 Monoamine Oxidase Inhibitors (MAOIs) The use of MAOIs intended to treat psychiatric disorders with olanzapine and fluoxetine capsules or within 5 weeks of stopping treatment with olanzapine and fluoxetine capsules is contraindicated because…
Other Contraindications Pimozide [see Warnings and Precautions ( 5.20 ) and Drug Interactions ( 7.7 , 7.8 )] Thioridazine [see Warnings and Precautions ( 5.20 ) and Drug Interactions ( 7.7 , 7.8 )] Pimozide and thioridazine prolong the QT interval.
Olanzapine and fluoxetine capsules can increase the levels of pimozide and thioridazine through inhibition of CYP2D6.
Pimozide and thioridazine are contraindicated for use with olanzapine and fluoxetine capsules.
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.