Clemastine and Acetaminophen And Codeine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jun 30, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Clemastine
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.
Your pain medicine contains codeine, an opioid that naturally slows down your gut and can make it hard to pee. Clemastine is an antihistamine with drying (anticholinergic) effects that also slow the gut and bladder. Taken together, these two can add up and cause severe constipation or trouble urinating. In rare cases, the bowel can slow so much that it nearly stops, which is called paralytic ileus.
This concern is based on how these drugs work rather than lots of real-world reports, so it may never affect you. Still, please watch for a bloated belly, no bowel movements, or trouble peeing, and let your pharmacist or doctor know. They can easily help you manage this.
Effect: Additive anticholinergic and opioid-mediated slowing of GI and urinary motility, increasing risk of severe constipation, urinary retention, and potentially paralytic ileus.
Mechanism: Codeine (opioid) reduces gut motility; clemastine (H1 antihistamine with anticholinergic activity) further impairs smooth-muscle motility. Pharmacodynamic, additive.
Direction/magnitude: Increased constipating/retentive effect; magnitude not quantified.
Evidence: Theoretical. Onset: unspecified. Severity: major.
- Monitor for reduced bowel sounds, abdominal distension, absent stool, and urinary retention.
- Consider stool softener/bowel regimen and dose individualization by the care team.
What happens
An increased risk of paralytic ileus
Interaction Deep Dive
Concomitant use of codeine with anticholinergic drugs may increase the risk of urinary retention and/or severe constipation, which may lead to paralytic ileus. Monitor patients for signs of urinary retention or reduced gastric motility when codeine is used concomitantly with anticholinergic drugs1.
Why it happens (mechanism)
Additive effects on gastric motility
How to manage this interaction
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. Your care team can manage this by monitoring you and tailoring your regimen.
- Watch for warning signs: constipation, a swollen or painful belly, no bowel movements for a few days, or trouble urinating.
- Report these promptly to your pharmacist or doctor.
- Stay hydrated and keep moving as you are able; your team may suggest a bowel regimen.
- Your doses may need to be adjusted and individualized, or an alternative antihistamine considered, by your care team.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Clemastine and Acetaminophen And Codeine together?
Combining codeine with clemastine can add up to cause severe constipation or trouble urinating, and rarely a near-stopped bowel; watch for these symptoms and tell your pharmacist or doctor if they appear. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Clemastine and Acetaminophen And Codeine 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 is the Clemastine and Acetaminophen And Codeine interaction managed?
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. Your care team can manage this by monitoring you and tailoring your regimen. Watch for warning signs: constipation, a swollen or painful belly, no bowel movements for a few days, or trouble urinating. Report these promptly to your pharmacist or doctor. Stay hydrated and keep moving as you are able; your team may s… Management is individual — always follow your own care team's guidance.
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 Clemastine or Acetaminophen And Codeine 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: CARISOPRODOL, ASPIRIN, CODEINE PHOSPHATE oral tablets, carisoprodol, aspirin, codeine phosphate oral tablets. Ingenus Pharmaceuticals LLC (per DailyMed), Orlando, FL, 2021. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Clemastine
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