Drug interactions

Chlorzoxazone + Levorphanol

Severity: Major

Chlorzoxazone and Levorphanol: major interaction.

Last updated 29 Oct 2026 Sources: US FDA label

For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.

Summary

Combining an opioid with a muscle relaxant raises the risk of profound sedation, respiratory depression, hypotension and coma. The risk is higher at high doses, in older adults and with other depressants.

Chlorzoxazone

What this interaction means in plain words

Chlorzoxazone and Levorphanol can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.

Evidence level: Moderate

Why it happens

Additive central nervous system and respiratory depression.

What to do

Reserve concurrent use for patients without alternatives, using the lowest effective doses and shortest duration. Monitor for sedation and respiratory depression.

What to ask your pharmacist

Does the benefit of taking both outweigh the risk in my case?
Do I need any blood test, ECG or other check while on both?
What early warning signs should I watch for, and what should I do if they appear?

Bring a full list of your medicines, including over-the-counter products, supplements and herbal remedies, to every pharmacy visit.

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References

Levorphanol Tartrate - FDA drug label (DailyMed) - section 7 Drug Interactions (class statement: muscle relaxants; "Levorphanol may enhance the neuromuscular blocking action of skeletal muscle relaxants and produce an increased degree of respiratory depression.") — DailyMed (FDA label)

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Frequently asked questions

Can I take Chlorzoxazone with Levorphanol?

MediHelp rates the interaction as major. Chlorzoxazone and Levorphanol can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Combining an opioid with a muscle relaxant raises the risk of profound sedation, respiratory depression, hypotension and coma. The risk is higher at high doses, in older adults and with other depressants.

How serious is the interaction between Chlorzoxazone and Levorphanol?

MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Reserve concurrent use for patients without alternatives, using the lowest effective doses and shortest duration. Monitor for sedation and respiratory depression.

What other medicines interact with Chlorzoxazone?

MediHelp also lists interactions of Chlorzoxazone with, for example, Alfentanil, Alprazolam, Amobarbital. The full list is on the Chlorzoxazone page.

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