What the FDA labels say about taking them together
Dextromethorphan/quinidine and thioridazine
Dextromethorphan/quinidine's FDA label of July 8, 2026 names thioridazine in its contraindications section; the thioridazine label PlainMeds reads does not name dextromethorphan/quinidine. The dextromethorphan/quinidine label: “Drugs that Prolong QT and are Metabolized by CYP2D6 Do not use with drugs that both prolong QT interval and are metabolized by CYP2D6.”
Check it at the source: the dextromethorphan/quinidine FDA label on DailyMed (effective July 8, 2026, Sun Pharmaceutical Industries, Inc.); the thioridazine FDA label on DailyMed (effective November 11, 2025, Mylan Institutional Inc.).
What does the dextromethorphan/quinidine label say about thioridazine?
Dextromethorphan/quinidine label, contraindicationsAllow 14 days after stopping dextromethorphan hydrobromide and quinidine sulfate before starting an MAOI. ( 4.3 ) Prolonged QT interval, congenital long QT syndrome, history suggestive of torsades de pointes, or heart failure. ( 4.4 ) Complete atrioventricular (AV) block without implanted pacemaker, or patients at high risk of complete AV block. ( 4.4 ) Concomitant use with drugs that both prolong QT interval and are metabolized by CYP2D6 (e.g., thioridazine or pimozide).
Dextromethorphan/quinidine label, drug interactionsDrugs that Prolong QT and are Metabolized by CYP2D6 Do not use with drugs that both prolong QT interval and are metabolized by CYP2D6 (e.g., thioridazine or pimozide) [see Contraindications (4.4) ].
Source: FDA drug label (Nuedexta, NDA021879), Otsuka America Pharmaceutical, Inc, effective January 22, 2026 (SPL set c8cce784-8c5f-415b-8068-76e5d481d159), via openFDA
Source: FDA drug label (Dextromethorphan Hydrobromide and Quinidine Sulphate), Sun Pharmaceutical Industries, Inc., effective July 8, 2026 (SPL set 92b54ac4-594e-47b8-a4d3-394a29b425f3), via openFDA; the full label on DailyMed
What does the thioridazine label say about dextromethorphan/quinidine?
Thioridazine's label (effective November 11, 2025) does not name dextromethorphan/quinidine in these sections. A label lists what its studies and reports found; it is not a complete list.
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
| Dextromethorphan/quinidine | Thioridazine | |
|---|---|---|
| Labeled for | n/a | n/a |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $26.64 per capsule 20-10 mg capsule | $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