Drug Interaction Report

Thioridazine and Morphine Injection: Interaction Details

A pharmacist-reviewed analysis of the Thioridazine 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

Thioridazine

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 117 documented Thioridazine interactions, 49 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 and an increased risk of profound sedation, respiratory depression, hypotension, coma

Interaction Deep Dive

Reserve the concomitant use of morphine and anticholinergic CNS depressants to patients for whom alternatives are inadequate. If concomitant use is necessary, use the lowest dose and shortest duration necessary to achieve treatment goals. Also, concomitant use may result in increased urinary retention or severe constipation, which may lead to paralytic ileus. Consider using a lower dose of morphine or the CNS depressant and closely monitor for urinary retention, severe constipation, sedation, and respiratory depression432. If Morphabond ER(TM) is being initiated, start at the lowest possible dose, 15 mg every 12 hours, and consider using a lower dosage of the concomitant CNS depressant 5. The risk of opioid overdose is increased with concurrent use of morphine with CNS depressants. Consider prescribing naloxone for the emergency treatment of opioid overdose 1.

Why it happens (mechanism)

Additive effects on gastric motility; additive CNS depression

Common questions

Can I take Thioridazine and Morphine Injection together?

Increased risk of urinary retention, severe constipation, and paralytic ileus and an increased risk of profound sedation, respiratory depression, hypotension, coma Always confirm with your pharmacist or prescriber before making any change.

How serious is the Thioridazine 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 Thioridazine 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 (5)

  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: DURAMORPH intravenous, epidural, intrathecal injection, morphine sulfate intravenous, epidural, intrathecal injection. Hikma Pharmaceuticals USA Inc (Per FDA), Berkeley, NJ, 2023. DailyMed
  3. Product Information: KADIAN(R) oral extended-release capsules, morphine sulfate oral extended-release capsules. Allergan USA, Inc (per FDA), Irvine, CA, 2016. DailyMed
  4. Product Information: ARYMO(TM) ER oral extended-release tablets, morphine sulfate oral extended-release tablets. Egalet US Inc (per manufacturer), Wayne, PA, 2017. DailyMed
  5. Product Information: MORPHABOND(TM) ER oral extended-release tablets, morphine sulfate oral extended-release tablets. Daiichi Sankyo Inc (per FDA), Basking Ridge, NJ, 2018. DailyMed
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Thioridazine

Keep reading about Thioridazine

All Thioridazine interactions (117)
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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:

Thioridazine + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Henbane Indian Snakeroot + 160 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.