Drug interactions
Diphenhydramine + Quazepam
Severity: Major
Diphenhydramine and Quazepam: major interaction.
Last updated 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
Quazepam is a long-acting benzodiazepine hypnotic, and combining it with diphenhydramine increases sedation, next-day impairment and fall risk. Respiratory depression may occur in vulnerable patients.
What this interaction means in plain words
Diphenhydramine and Quazepam 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.
Why it happens
Additive CNS depression from GABA-A potentiation and central H1 blockade.
What to do
Avoid concurrent use where possible, especially in older adults. If both are required, use the lowest doses and monitor for oversedation 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?
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References
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Quazepam?
MediHelp rates the interaction as major. Diphenhydramine and Quazepam 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. Quazepam is a long-acting benzodiazepine hypnotic, and combining it with diphenhydramine increases sedation, next-day impairment and fall risk. Respiratory depression may occur in vulnerable patients.
How serious is the interaction between Diphenhydramine and Quazepam?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid concurrent use where possible, especially in older adults. If both are required, use the lowest doses and monitor for oversedation and respiratory depression.
What other medicines interact with Diphenhydramine?
MediHelp also lists interactions of Diphenhydramine with, for example, Alfentanil, Belladonna and opium, Benzhydrocodone / acetaminophen. The full list is on the Diphenhydramine page.
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