What the FDA labels say about taking them together
Clozapine and thioridazine
Clozapine's FDA label of June 6, 2025 names thioridazine in its drug interactions section; thioridazine's label does not name clozapine itself but warns about its class (Atypical antipsychotics). The clozapine label: “Drugs that cause QT prolongation include: specific antipsychotics, specific antibiotics, Class 1A antiarrhythmics or Class III antiarrhythmics, and others.”
Check it at the source: the clozapine FDA label on DailyMed (effective June 6, 2025, HLS Therapeutics (USA), Inc.); the thioridazine FDA label on DailyMed (effective November 11, 2025, Mylan Institutional Inc.).
What does the clozapine label say about thioridazine?
Clozapine label, drug interactionsDrugs that cause QT prolongation include: specific antipsychotics (e.g., ziprasidone, iloperidone, chlorpromazine, thioridazine, mesoridazine, droperidol, and pimozide), specific antibiotics (e.g., erythromycin, gatifloxacin, moxifloxacin, sparfloxacin), Class 1A antiarrhythmics (e.g., quinidine, procainamide) or Class III antiarrhythmics (e.g., amiodarone, sotalol), and others (e.g., pentamidine, levomethadyl acetate, methadone, halofantrine, mefloquine, dolasetron mesylate, probucol or tacrolimus) [see Warnings and Precautions ( 5.9 )].
Source: FDA drug label (Clozaril), NDA019758 (Heritage Life), as published by HLS Therapeutics (USA), Inc., effective June 6, 2025 (SPL set 90876802-0e3a-44c9-9ff7-1754dfbe736a), via openFDA; the full label on DailyMed
What does the thioridazine label say about clozapine?
Thioridazine's label does not name clozapine itself; it warns about its class (Atypical antipsychotics):
Thioridazine label, boxed warningAnalyses of seventeen placebo-controlled trials (modal duration of 10 weeks), largely in patients taking atypical antipsychotic drugs, revealed a risk of death in drug-treated patients of between 1.6 to 1.7 times the risk of death in placebo-treated patients.
Thioridazine label, boxed warningDue to its potential for significant, possibly life threatening, 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 , and INDICATIONS ).
Source: FDA drug label (Thioridazine Hydrochloride), Mylan Institutional Inc., effective November 11, 2025 (SPL set 52fea941-0b47-41c1-b00d-f88150e8ab93), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Clozapine | Thioridazine | |
|---|---|---|
| Labeled for | Schizophrenia | n/a |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.610 per tablet 100 mg tablet | $0.571 per tablet 25 mg tablet |
| Shortage now | No current entry | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once