Duloxetine and Acetaminophen And Codeine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 1, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Duloxetine
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 prodrug. That means your body has to turn it into morphine (using a liver enzyme called CYP2D6) before it can relieve pain. Duloxetine can slow that enzyme down, so you may make less morphine and get less pain relief. If you have been taking codeine for a while, this could even bring on withdrawal-type feelings.
There is a second concern: both drugs affect serotonin, a brain chemical. Together they can rarely cause serotonin syndrome (agitation, shivering, fast heartbeat, sweating). The good news is your care team can manage this by watching you closely and tailoring your doses. Keep taking both as prescribed and check in with them.
Direction: Codeine is a prodrug requiring CYP2D6 activation to morphine. Duloxetine, a moderate CYP2D6 inhibitor, reduces morphine formation, increasing parent codeine exposure and lowering active metabolite (morphine) AUC/Cmax, potentially reducing analgesia or precipitating withdrawal in dependent patients.
Plus PD interaction: additive serotonergic activity raises serotonin syndrome risk.
- Evidence: theoretical; severity: major; onset: unspecified.
- Monitor for reduced efficacy/withdrawal; codeine dose may be individualized upward if needed.
- On duloxetine discontinuation, anticipate increased morphine formation; dose may need reduction with monitoring for respiratory depression.
- Observe for serotonin syndrome, especially at initiation/titration; discontinue codeine if suspected.
What happens
Increased risk of serotonin syndrome, increased codeine exposure and reduced active metabolite (morphine) exposure
Interaction Deep Dive
Concomitant use of codeine and a CYP2D6 inhibitor may reduce plasma concentrations of morphine, the active metabolite of codeine, thus potentially leading to reduced efficacy or onset of a withdrawal syndrome in patients who have developed physical dependence. If concomitant use is necessary, monitor patients for withdrawal symptoms and consider increasing the codeine dose. Once the CYP2D6 inhibitor is discontinued, consider reducing the codeine dose and monitor for respiratory depression. Additionally, concomitant use of opioids with serotonergic drugs has resulted in serotonin syndrome. If concomitant use is needed, carefully observe the patient, particularly during treatment initiation and dose adjustments. Discontinue codeine if serotonin syndrome is suspected12.
Why it happens (mechanism)
Additive serotonergic effects; inhibition of CYP2D6-mediated codeine metabolism
How to manage this interaction
Do not stop or change either medicine on your own. Both can be used together when your care team keeps an eye on things.
- Watch for less pain relief or withdrawal-type symptoms; your team may adjust and individualize your codeine dose if needed.
- If your duloxetine is stopped later, tell your prescriber, since your codeine dose may need to be lowered and you may be watched for slowed breathing.
- Get urgent help for signs of serotonin syndrome: agitation, shivering, sweating, fast heartbeat, muscle twitching, or confusion.
- Raise any concerns with your pharmacist or prescriber.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Duloxetine and Acetaminophen And Codeine together?
Duloxetine can blunt codeine's pain relief (by lowering morphine formation) and together they slightly raise the risk of serotonin syndrome, but your care team can manage this with monitoring and dose adjustment. Report reduced pain control or symptoms like agitation, shivering, or fast heartbeat. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Duloxetine and Acetaminophen And Codeine 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 Duloxetine and Acetaminophen And Codeine interaction managed?
Do not stop or change either medicine on your own. Both can be used together when your care team keeps an eye on things. Watch for less pain relief or withdrawal-type symptoms; your team may adjust and individualize your codeine dose if needed. If your duloxetine is stopped later, tell your prescriber, since your codeine dose may need to be lowered and you may be watched for slowed breathing. Get… 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 Duloxetine or Acetaminophen And Codeine 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 (2)
- 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
Keep reading about Acetaminophen And Codeine
Keep reading about Duloxetine
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