Drug Interaction Report

Amantadine and Morphine Injection: Interaction Details

A pharmacist-reviewed analysis of the Amantadine and Morphine Injection interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Amantadine

No brand names on record
+

Morphine Injection

Astramorph® PF Duramorph Duramorph® Infumorph Infumorph® Kadian Mitigo MS Contin
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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.

Of 22 documented Amantadine interactions, 22 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

Increased risk of urinary retention, severe constipation, and paralytic ileus

Interaction Deep Dive

Coadministration of morphine and an anticholinergic agent may result in increased urinary retention or severe constipation, which may lead to paralytic ileus. If concomitant use is required, monitor patients for signs of urinary retention and reductions in gastric motility6154327.

Why it happens (mechanism)

Additive effects on gastric motility

Common questions

Can I take Amantadine and Morphine Injection together?

Increased risk of urinary retention, severe constipation, and paralytic ileus Always confirm with your pharmacist or prescriber before making any change.

How serious is the Amantadine and Morphine Injection 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.

Questions for your pharmacist

  • Does my dose of Amantadine or Morphine Injection 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)

  1. Product Information: MS CONTIN(R) oral extended-release tablets, morphine sulfate oral extended-release tablets. Purdue Pharma LP (per FDA), Stamford, CT, 2023. DailyMed
  2. Product Information: INFUMORPH intrathecal, epidural injection, morphine sulfate intrathecal, epidural injection. Hikma Pharmaceuticals USA Inc (per FDA), Berkeley Heights, NJ, 2023. DailyMed
  3. Product Information: Morphine sulfate oral tablets, morphine sulfate oral tablets. Hikma Pharmaceuticals USA Inc.(Per FDA), Berkeley, NJ, 2023. DailyMed
  4. Product Information: Morphine sulfate oral solution, morphine sulfate oral solution. Hikma Pharmaceuticals USA Inc (per FDA), Berkeley Heights, NJ, 2023. DailyMed
  5. Product Information: DURAMORPH intravenous, epidural, intrathecal injection, morphine sulfate intravenous, epidural, intrathecal injection. Hikma Pharmaceuticals USA Inc (Per FDA), Berkeley, NJ, 2023. DailyMed
  6. Product Information: KADIAN(R) oral extended-release capsules, morphine sulfate oral extended-release capsules. Allergan USA, Inc (per FDA), Madison, NJ, 2019. DailyMed
  7. Product Information: Morphine sulfate intravenous injection, morphine sulfate intravenous injection. Mallinckrodt Inc (Per FDA), St. Louis, MO, 2023. DailyMed
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Amantadine

Keep reading about Amantadine

All Amantadine interactions (22)
Also serious with: Acetaminophen And Codeine Diphenhydramine Injection Memantine Trospium / Xanomeline
Morphine Injection

Keep reading about Morphine Injection

All Morphine Injection interactions (437) Morphine Injection drug information
Also serious with: Rasagiline Procarbazine Phenelzine Ozanimod
Beyond drug–drug

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:

Amantadine + Activated Charcoal Henbane Scopolia Angel's Trumpet Bacopa Belladonna Betel Nut Boxwood + 38 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.