Acetaminophen And Codeine and Quinine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Quinine
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
Your pain medicine contains codeine, which is a bit unusual. Codeine itself does not do much for pain until your body turns it into morphine, using an enzyme called CYP2D6. That morphine is what actually eases your pain.
Quinine can slow down that enzyme. So when you take both, your body may make less morphine, which means the codeine may not relieve your pain as well as usual. If you already take codeine regularly, you might even feel some withdrawal-type discomfort. The good news: this is mostly a theoretical concern, and your care team can manage it by watching how you feel and adjusting your dose if needed. Please don't change anything on your own.
Mechanism: Quinine inhibits CYP2D6, the enzyme that O-demethylates codeine (a prodrug) to its active metabolite morphine. Inhibition raises parent codeine exposure but reduces morphine formation.
- Direction: reduced analgesic efficacy; possible withdrawal in opioid-dependent patients.
- Evidence: theoretical; severity rated major.
- Onset: unspecified.
- Management: if co-administration is necessary, monitor for withdrawal and inadequate analgesia; the codeine dose may be adjusted and individualized by the care team. On stopping quinine, reduce codeine dose and monitor for sedation and respiratory depression as morphine formation recovers.
What happens
Increased codeine exposure and reduced active metabolite (morphine) exposure
Interaction Deep Dive
Taking codeine together with a CYP2D6 inhibitor can lower the plasma levels of morphine, which is the active metabolite produced from codeine, and this may result in diminished effectiveness along with withdrawal symptoms. When these agents must be given together, watch patients for withdrawal symptoms and think about raising the codeine dose. After the CYP2D6 inhibitor is stopped, consider lowering the codeine dose while observing for signs and symptoms of sedation and respiratory depression312.
Why it happens (mechanism)
Inhibition of CYP2D6-mediated codeine metabolism
How to manage this interaction
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Because quinine can lower how much active pain reliever (morphine) your body makes from codeine, here is what your team may do:
- Watch whether your pain relief seems weaker than expected.
- Watch for any withdrawal-type symptoms if you use codeine regularly.
- Adjust and individualize your codeine dose if needed.
- Re-check your dose when quinine is stopped, since your pain relief (and side effects like drowsiness or slowed breathing) may increase again.
Tell your pharmacist or prescriber if your pain is not controlled or if you feel unwell on this combination.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Quinine together?
Quinine can slow the enzyme that turns codeine into morphine, so your codeine may work less well; keep taking both as prescribed and let your care team know if your pain isn't controlled so they can adjust and monitor. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Quinine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Acetaminophen And Codeine and Quinine interaction managed?
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Because quinine can lower how much active pain reliever (morphine) your body makes from codeine, here is what your team may do: Watch whether your pain relief seems weaker than expected. Watch for any withdrawal-type symptoms if you use codeine regularly. Adjust and individualize your codeine dose if needed… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Acetaminophen And Codeine or Quinine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (3)
- Product Information: Codeine sulfate oral solution, codeine sulfate oral solution. Hikma Pharmaceuticals USA Inc(per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: Codeine sulfate oral tablets, codeine sulfate oral tablets. Hikma Pharmaceuticals USA Inc. (per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: codeine sulfate oral tablets, codeine sulfate oral tablets. West-Ward Pharmaceuticals Corp. (per FDA), Eatontown, NJ, 2017. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Quinine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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