Morphine Injection and Paroxetine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Paroxetine
Morphine Injection
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.
What happens
Increased QT interval prolongation, increased morphine exposure, increased risk of urinary retention, constipation, paralytic ileus and an increased risk of serotonin syndrome
Interaction Deep Dive
Concomitant use of morphine with PARoxetine (serotonergic P-gp inhibitor) may increase the exposure of morphine by two-fold, increase the risk of adverse effects, including respiratory, CNS depression and it has also resulted in serotonin syndrome. If coadministration is required, monitor for signs of CNS depression. Evaluate patients for signs of respiratory depression that may be greater than otherwise expected and decrease the dosage of morphine and/or P-gp inhibitor as necessary. Additionally, concomitant use of morphine with PARoxetine (anticholinergic drug) may increase the risk of urinary retention and severe constipation, which may lead to paralytic ileus. If concomitant use is needed, carefully observe the patient, particularly during treatment initiation and dose adjustments for serotonin syndrome and observe for signs and symptoms of urinary retention or reduced gastric motility. Discontinue morphine if serotonin syndrome is suspected4132.
Why it happens (mechanism)
Additive QT interval prolongation; inhibition of P-gp-mediated efflux transport of morphine; additive effects on gastric motility; additive serotonergic effects
Literature reports
1 report — tap to read
Common questions
Can I take Morphine Injection and Paroxetine together?
Increased QT interval prolongation, increased morphine exposure, increased risk of urinary retention, constipation, paralytic ileus and an increased risk of serotonin syndrome Always confirm with your pharmacist or prescriber before making any change.
How serious is the Morphine Injection 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 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 Morphine Injection 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 (4)
- Product Information: MS CONTIN(R) oral extended-release tablets, morphine sulfate oral extended-release tablets. Purdue Pharma LP (per FDA), Stamford, CT, 2023. DailyMed
- Product Information: INFUMORPH intrathecal, epidural injection, morphine sulfate intrathecal, epidural injection. Hikma Pharmaceuticals USA Inc (per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: Morphine sulfate oral solution, morphine sulfate oral solution. Hikma Pharmaceuticals USA Inc (per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: DURAMORPH intravenous, epidural, intrathecal injection, morphine sulfate intravenous, epidural, intrathecal injection. Hikma Pharmaceuticals USA Inc (Per FDA), Berkeley, NJ, 2023. DailyMed
Keep reading about Paroxetine
Keep reading about Morphine Injection
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist