Morphine Injection and Carisoprodol: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Carisoprodol
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 risk of urinary retention, severe constipation, and paralytic ileus, an increased risk of profound sedation, hypotension, coma and an increased risk respiratory depression
Interaction Deep Dive
Concomitant use of morphine and anticholinergic CNS depressants concomitant use may result in increased risk of profound sedation, hypotension, coma, opioid overdose and urinary retention or severe constipation, which may lead to paralytic ileus. Concomitant use of morphine with skeletal muscle relaxants may enhance the neuromuscular blocking action of muscle relaxants and produce an increased degree of respiratory depression. Reserve the concomitant use to patients for whom alternatives are inadequate. Monitor patients for signs of respiratory depression that may be greater than otherwise expected and decrease the dosage of morphine and/or the muscle relaxant as necessary. If concomitant use is necessary, use the lowest dose and shortest duration necessary to achieve treatment goals. Consider using a lower dose of morphine or the CNS depressant and closely monitor for urinary retention, severe constipation, sedation. The risk of opioid overdose is increased with concurrent use of morphine with CNS depressants. Consider prescribing naloxone for the emergency treatment of opioid overdose312.
Why it happens (mechanism)
Additive effects on gastric motility; additive CNS depression; enhanced neuromuscular blockade
Common questions
Can I take Morphine Injection and Carisoprodol together?
Increased risk of urinary retention, severe constipation, and paralytic ileus, an increased risk of profound sedation, hypotension, coma and an increased risk respiratory depression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Morphine Injection and Carisoprodol 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 Morphine Injection or Carisoprodol 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 (3)
- 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: DURAMORPH intravenous, epidural, intrathecal injection, morphine sulfate intravenous, epidural, intrathecal injection. Hikma Pharmaceuticals USA Inc (Per FDA), Berkeley, NJ, 2023. DailyMed
Keep reading about Carisoprodol
Keep reading about Morphine Injection
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