Morphine and Amitriptyline: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Amitriptyline
Morphine
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.
Taking amitriptyline (Elavil) and morphine together can add up in two ways. First, both can slow down your gut and bladder, so you may notice severe constipation or trouble urinating. In rare cases, a very slow gut can lead to a serious blockage. Second, both can raise a brain chemical called serotonin, and together they can occasionally cause a reaction called serotonin syndrome (things like shakiness, sweating, a fast heartbeat, agitation, or fever).
This is mostly a theoretical concern, and many people take these safely. The good news is your care team can manage this by watching you closely, especially when you first start or change a dose.
Additive PD interaction between amitriptyline (TCA) and morphine, two directions:
- Serotonergic: both increase serotonergic tone, raising theoretical risk of serotonin syndrome.
- Anticholinergic/GI: amitriptyline's antimuscarinic effects plus morphine's opioid effect on gut motility increase risk of urinary retention, severe constipation, and paralytic ileus.
Evidence: theoretical. Onset: unspecified. Neither is a relevant prodrug here; this is a pharmacodynamic, not PK, interaction. Management: if co-prescribed, monitor closely at initiation and dose changes for serotonin toxicity (autonomic instability, clonus, hyperthermia, altered mental status) and for reduced GI motility/urinary retention. Discontinue morphine if serotonin syndrome is suspected.
What happens
Increased risk of urinary retention, severe constipation, paralytic ileus and an increased risk of serotonin syndrome
Interaction Deep Dive
Serotonin syndrome has occurred when opioids like morphine are taken together with serotonergic agents. Furthermore, combining morphine with anticholinergic medications can heighten the likelihood of urinary retention and severe constipation, potentially progressing to paralytic ileus. When such combined use cannot be avoided, monitor the patient closely, especially when starting therapy and modifying doses, watching for serotonin syndrome as well as any indications of urinary retention or diminished gastric motility. Should serotonin syndrome be suspected, stop morphine1234567.
Why it happens (mechanism)
Additive effects on gastric motility; additive serotonergic effects
How to manage this interaction
If both drugs are prescribed, keep taking them as directed unless your prescriber tells you otherwise. Your care team can manage this by watching you more closely, especially when starting either drug or changing a dose, and doses may be adjusted and individualized for you.
Contact your pharmacist or prescriber if you notice:
- Trouble urinating or being unable to pass urine
- Severe constipation, belly pain, bloating, or no bowel movements
- Serotonin syndrome signs: agitation, sweating, tremor, muscle twitching, fast heartbeat, or fever
Seek urgent care for severe symptoms. Your team may stop the morphine if serotonin syndrome is suspected.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
Common questions
Can I take Morphine and Amitriptyline together?
Using amitriptyline with morphine can add up to cause constipation, trouble urinating, or rarely serotonin syndrome; keep taking both as prescribed but watch for these symptoms and tell your care team right away. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Morphine and Amitriptyline 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 Morphine and Amitriptyline interaction managed?
If both drugs are prescribed, keep taking them as directed unless your prescriber tells you otherwise. Your care team can manage this by watching you more closely, especially when starting either drug or changing a dose, and doses may be adjusted and individualized for you. Contact your pharmacist or prescriber if you notice: Trouble urinating or being unable to pass urine Severe constipation, bel… 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 Morphine or Amitriptyline 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 (7)
- Product Information: KADIAN(R) oral extended-release capsules, morphine sulfate oral extended-release capsules. Allergan USA, Inc (per FDA), Madison, NJ, 2019. DailyMed
- Product Information: DURAMORPH intravenous, epidural, intrathecal injection, morphine sulfate intravenous, epidural, intrathecal injection. Hikma Pharmaceuticals USA Inc (Per FDA), Berkeley, NJ, 2023. DailyMed
- 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: Morphine sulfate oral solution, morphine sulfate oral solution. Hikma Pharmaceuticals USA Inc (per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: Morphine sulfate oral tablets, morphine sulfate oral tablets. Hikma Pharmaceuticals USA Inc.(Per FDA), Berkeley, NJ, 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 intravenous injection, morphine sulfate intravenous injection. Mallinckrodt Inc (Per FDA), St. Louis, MO, 2023. DailyMed
Keep reading about Amitriptyline
Keep reading about Morphine
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