Acetaminophen And Codeine and Trospium: 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
Trospium
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.
Here's what's going on. Codeine (the pain part of your acetaminophen-codeine pill) can slow down your gut and make it harder to pee. Trospium is a bladder medicine that works by blocking a body signal called acetylcholine, and one of its effects is also to slow the gut and reduce urination. When you take both, those slowing effects can stack up.
In rare cases, a badly slowed gut can nearly stop moving, which is a serious problem called paralytic ileus. The good news is this is uncommon and based on how these drugs work, not on lots of real cases. Watch for bad constipation or trouble urinating, and your care team can manage this easily.
Mechanism: additive anticholinergic and opioid effects on GI and urinary smooth muscle. Codeine (an opioid; note it is a prodrug activated by CYP2D6 to morphine, but that is not relevant here) reduces gastric motility, and trospium, a quaternary anticholinergic antimuscarinic, does the same, plus both promote urinary retention.
- Direction: additive PD effect, increased constipation/urinary retention risk, potential paralytic ileus.
- Severity: major; evidence: theoretical; onset: unspecified.
- Management: monitor for reduced bowel motility, abdominal distension, and urinary retention. Consider bowel regimen; individualize dosing.
What happens
An increased risk of paralytic ileus
Interaction Deep Dive
Taking codeine at the same time as anticholinergic medications can heighten the likelihood of urinary retention and/or serious constipation, potentially progressing to paralytic ileus. When codeine is combined with anticholinergic agents, watch patients for indications of urinary retention or diminished gastric motility1.
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. This combination is manageable with a little attention.
- Watch for severe constipation, belly bloating or pain, or trouble urinating, and report these promptly.
- Your care team may monitor you more closely and can adjust or individualize your doses if needed.
- Staying hydrated and staying active can help keep your bowels moving; ask your pharmacist whether a stool softener is appropriate for you.
- Call your doctor right away if you stop having bowel movements or cannot pass gas.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Trospium together?
Codeine and trospium can both slow your gut and bladder, so together they raise the risk of severe constipation, urinary retention, or rarely a stalled bowel; keep taking both as prescribed but tell your care team about bad constipation or trouble urinating. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Trospium 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 Acetaminophen And Codeine and Trospium interaction managed?
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. This combination is manageable with a little attention. Watch for severe constipation, belly bloating or pain, or trouble urinating, and report these promptly. Your care team may monitor you more closely and can adjust or individualize your doses if needed. Staying hydrated and staying active can help keep your bo… 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 Acetaminophen And Codeine or Trospium 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 Trospium
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