Hydromorphone Injection and Chlorzoxazone: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Chlorzoxazone
Hydromorphone 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 profound sedation, respiratory depression, coma and death
Interaction Deep Dive
Concomitant use of HYDROmorphone with drugs that are skeletal muscle relaxants and CNS depressants can increase the risk of hypotension, respiratory depression, profound sedation, coma, and death. Reserve the concomitant use of HYDROmorphone and 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. Consider using a lower dose of HYDROmorphone or the CNS depressant. Monitor patients closely for sings and symptoms of sedation and respiratory depression. Respiratory depression may be greater than otherwise expected with concomitant skeletal muscle relaxant and hence decrease the dosage of HYDROmorphone and/or the muscle relaxant as necessary. If concomitant use is warranted, consider prescribing naloxone for the emergency treatment of opioid overdose12
Why it happens (mechanism)
Enhanced neuromuscular blockade; additive CNS depression
Literature reports
1 report — tap to read
a) Observational studies have demonstrated that concomitant use of opioid analgesics and benzodiazepines increases the risk of drug-related mortality compared to use of opioid analgesics alone. Because of similar pharmacological properties, it is reasonable to expect similar risk with the concomitant use of other CNS depressant drugs with opioid analgesics 12.
Common questions
Can I take Hydromorphone Injection and Chlorzoxazone together?
Increased risk of profound sedation, respiratory depression, coma and death Always confirm with your pharmacist or prescriber before making any change.
How serious is the Hydromorphone Injection and Chlorzoxazone 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 Hydromorphone Injection or Chlorzoxazone 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 (2)
- Product Information: DILAUDID(R) oral tablets, oral solution, hydromorphone HCl oral tablets, oral solution. Rhodes Pharmaceuticals LP (per FDA), Wilson, NC, 2023. DailyMed
- Product Information: DILAUDID(R) intravenous injection, intramuscular injection, subcutaneous injection, hydromorphone HCl intravenous injection, intramuscular injection, subcutaneous injection. Fresenius Kabi. (per FDA), Lake Zurich, IL, 2023. DailyMed
Keep reading about Chlorzoxazone
Keep reading about Hydromorphone 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.
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