Diphenhydramine Topical and Dihydrocodeine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Diphenhydramine Topical
Dihydrocodeine
No brand names on record
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 paralytic ileus and an increased risk of respiratory and CNS depression
Interaction Deep Dive
Concomitant use of dihydrocodeine and anticholinergic CNS depressants may result in increased risk of urinary retention or severe constipation, which may lead to paralytic ileus and an increased risk of hypotension, respiratory depression, profound sedation, coma, and death. Reserve the concomitant use of dihydrocodeine 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 dihydrocodeine or the CNS depressant and closely monitor for urinary retention, severe constipation, sedation and respiratory depression. If concomitant use is warranted, consider prescribing naloxone for the emergency treatment of opioid overdose. Inform and educate the patients and caregivers on the signs and symptoms of respiratory depression (including sedation)1.
Why it happens (mechanism)
Unknown; 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 1.
Common questions
Can I take Diphenhydramine Topical and Dihydrocodeine together?
Increased risk of paralytic ileus and an increased risk of respiratory and CNS depression Always confirm with your pharmacist or prescriber before making any change.
How serious is the Diphenhydramine Topical and Dihydrocodeine 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 Diphenhydramine Topical or Dihydrocodeine 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 (1)
- Product Information: SYNALGOS(R)-DC oral capsules, aspirin, caffeine, dihydrocodeine bitartrate oral capsules. Sun Pharmaceuticals Industries Inc (per FDA), Cranbury, NJ, 2023. DailyMed
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