Tapentadol and Diphenhydramine Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Tapentadol
Diphenhydramine 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
An increased risk of respiratory and CNS depression and an increased risk of paralytic ileus
Interaction Deep Dive
Concomitant use of tapentadol with other anticholinergic CNS depressants increases the risk of respiratory depression, profound sedation, coma, opioid overdose, death and urinary retention and/or severe constipation, which may lead to paralytic ileus. Reserve the concomitant use of tapentadol 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. In patients already receiving tapentadol, prescribe a lower initial dose of CNS depressant than indicated in the absence of an opioid, and titrate based on clinical response. If tapentadol is initiated in a patient already taking a CNS depressant, prescribe a lower initial dose of tapentadol, and titrate based on clinical response. If concomitant use is warranted, consider prescribing naloxone for the emergency treatment of opioid overdose. Consider using a lower dose of tapentadol or the CNS depressant and closely monitor for urinary retention or reduced gastric motility, severe constipation, sedation, and respiratory depression12.
Why it happens (mechanism)
Additive CNS depression; additive effects on gastric motility
Common questions
Can I take Tapentadol and Diphenhydramine Injection together?
An increased risk of respiratory and CNS depression and an increased risk of paralytic ileus Always confirm with your pharmacist or prescriber before making any change.
How serious is the Tapentadol and Diphenhydramine 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 Tapentadol or Diphenhydramine 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 (2)
- Product Information: NUCYNTA(R) ER oral extended-release tablets, tapentadol oral extended-release tablets. Collegium Pharmaceutical Inc (per FDA), Stoughton, MA, 2023. DailyMed
- Product Information: NUCYNTA(R) oral tablets, tapentadol oral tablets. Collegium Pharmaceutical Inc (per FDA), Stoughton, MA, 2023. DailyMed
Keep reading about Tapentadol
Keep reading about Diphenhydramine Injection
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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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