Acetaminophen And Codeine and Paroxetine: 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
Paroxetine
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 your body has to turn into morphine to actually relieve pain. It uses a liver enzyme called CYP2D6 to do this. Paroxetine (Paxil) blocks that enzyme, so less of your codeine gets changed into the active painkiller. That means the codeine may not work as well, and you could even feel opioid withdrawal.
Two other things can happen. Both drugs can slow your gut and bladder, raising the risk of bad constipation or trouble urinating. And both affect serotonin, so together there is a small chance of a reaction called serotonin syndrome (agitation, sweating, shaking, fast heartbeat). This is mostly a theoretical concern, and your care team can manage it. Keep taking both as prescribed and let them know how you feel.
Direction: Codeine is a prodrug requiring CYP2D6 activation to morphine. Paroxetine is a potent CYP2D6 inhibitor, so it reduces morphine formation, lowering analgesic efficacy and risking opioid withdrawal, while raising parent codeine exposure.
- Additional mechanisms: additive anticholinergic effects on GI/bladder motility (constipation, urinary retention, paralytic ileus) and additive serotonergic effects (serotonin syndrome).
- Evidence: theoretical; severity major; onset unspecified.
- Management: monitor for reduced analgesia/withdrawal, severe constipation, urinary retention, respiratory depression, and serotonin syndrome during initiation and titration. Codeine dose may be adjusted with paroxetine; may require increase if paroxetine is stopped. Discontinue offending agent(s) and treat symptomatically if serotonin syndrome is suspected.
What happens
Increased risk of paralytic ileus, an increased risk of serotonin syndrome, an increased codeine exposure and reduced active metabolite (morphine) exposure
Interaction Deep Dive
Taking codeine together with PARoxetine (a serotonergic agent that has anticholinergic effects and inhibits CYP2D6) can lower plasma levels of morphine, the active metabolite of codeine. This may result in diminished efficacy and withdrawal symptoms, can raise the likelihood of urinary retention and severe constipation (which can progress to paralytic ileus), and can heighten the risk of serotonin syndrome. When the two must be given together, watch the patient carefully for withdrawal symptoms, urinary retention, severe constipation, respiratory depression, and any signs or symptoms of serotonin syndrome throughout treatment initiation and dose adjustment. Should serotonin syndrome be suspected, stop codeine1 and/or PARoxetine and begin symptomatic treatment. When PARoxetine is used concurrently, reduce the codeine dose (codeine being a CYP2D6 substrate) if necessary. On the other hand, the codeine dose may need to be raised if PARoxetine is stopped 23.
Why it happens (mechanism)
Additive effects on gastric motility; additive serotonergic effects; inhibition of CYP2D6-mediated codeine metabolism
How to manage this interaction
Both medicines can usually be used together when your care team is watching for a few things. This is a manageable situation.
- Keep taking both as prescribed unless your prescriber tells you otherwise.
- Tell your team if your pain relief seems weaker, or if you feel withdrawal-like symptoms (restlessness, sweating, chills).
- Watch for severe constipation, trouble urinating, or serotonin syndrome (agitation, shaking, fever, fast heartbeat) and report these promptly.
- Your codeine dose may be adjusted and individualized, and may need changing again if paroxetine is stopped.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Paroxetine together?
Paroxetine can make codeine less effective for pain (and cause withdrawal) while adding risks of severe constipation, urinary retention, and serotonin syndrome; keep taking both as prescribed and report weaker pain relief or these symptoms to your care team. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Paroxetine 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 Paroxetine interaction managed?
Both medicines can usually be used together when your care team is watching for a few things. This is a manageable situation. Keep taking both as prescribed unless your prescriber tells you otherwise. Tell your team if your pain relief seems weaker, or if you feel withdrawal-like symptoms (restlessness, sweating, chills). Watch for severe constipation, trouble urinating, or serotonin syndrome (agi… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Acetaminophen And Codeine or Paroxetine 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: CARISOPRODOL, ASPIRIN, CODEINE PHOSPHATE oral tablets, carisoprodol, aspirin, codeine phosphate oral tablets. Ingenus Pharmaceuticals LLC (per DailyMed), Orlando, FL, 2021. DailyMed
- Product Information: PEXEVA(R) oral tablets, paroxetine mesylate oral tablets. Sebela Pharmaceuticals Inc (per FDA), Roswell, GA, 2023.
- Product Information: PAXIL(R) oral tablets, oral suspension, paroxetine oral tablets, oral suspension. Apotex Corp (per FDA), Weston, FL, 2023. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Paroxetine
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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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