What the FDA labels say about taking them together
Codeine and quinidine
Codeine's FDA label of December 22, 2025 names quinidine in its drug interactions section, and quinidine's label names codeine too. The codeine label: “Codeine is metabolized by CYP2D6 to form morphine. The concomitant use of Codeine Sulfate Tablets and CYP2D6 inhibitors can increase the plasma concentration of codeine, but can decrease the plasma concentration of …”
Check it at the source: the codeine FDA label on DailyMed (effective December 22, 2025, Hikma Pharmaceuticals USA Inc.); the quinidine FDA label on DailyMed (effective February 1, 2018, Sun Pharmaceutical Industries, Inc.).
What does the codeine label say about quinidine?
Codeine label, drug interactionsRifampin, carbamazepine, phenytoin Inhibitors of CYP2D6 Clinical Impact: Codeine is metabolized by CYP2D6 to form morphine. The concomitant use of Codeine Sulfate Tablets and CYP2D6 inhibitors can increase the plasma concentration of codeine, but can decrease the plasma concentration of active metabolite morphine, which could result in reduced analgesic efficacy or symptoms of opioid withdrawal … intervals for signs and symptoms of respiratory depression or sedation. Paroxetine, fluoxetine, bupropion, quinidine.
Codeine label, warnings and precautionsRisks of Concomitant Use or Discontinuation of Cytochrome P450 2D6 Inhibitors: The concomitant use of Codeine Sulfate Tablets with all cytochrome P450 2D6 inhibitors (e.g., amiodarone, quinidine) may result in an increase in codeine plasma concentrations and a decrease in active metabolite morphine plasma concentration which could result in an analgesic efficacy reduction or symptoms of opioid withdrawal.
Source: FDA drug label (Codeine sulfate), Hikma Pharmaceuticals USA Inc., effective December 22, 2025 (SPL set 010905f9-3bcb-4b50-9fe8-a3ad0010f14c), via openFDA; the full label on DailyMed
What does the quinidine label say about codeine?
Quinidine label, drug interactionsIn the case of prodrugs whose actions are actually mediated by P450 IID6 -produced metabolites (for example, codeine and hydrocodone, whose analgesic and antitussive effects appear to be mediated by morphine and hydromorphone, respectively), it may not be possible to achieve the desired clinical benefits in poor metabolizers.
Source: FDA drug label (Quinidine Gluconate), Sun Pharmaceutical Industries, Inc., effective February 1, 2018 (SPL set 5023f053-fcc4-4c2c-aa59-9ec198ad185e), 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
| Codeine | Quinidine | |
|---|---|---|
| Labeled for | Pain | Atrial fibrillation |
| Boxed warning | Yes | Yes |
| Pharmacy cost (NADAC) | $0.726 per tablet 30 mg tablet | $4.92 per tablet 324 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