Fentanyl and Trospium / Xanomeline: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fentanyl
No brand names on recordTrospium / Xanomeline
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. Fentanyl is a strong opioid pain medicine, and it naturally slows down your gut and can make it harder to empty your bladder. Trospium (part of Cobenfy) is a bladder medicine that can have similar slowing effects. When you take both, those effects can add up. That means you may be more likely to get very constipated or have trouble passing urine. In rare cases, the gut can slow down so much that it stops moving, which is serious.
The good news is your care team can watch for this and manage it easily. Keep taking both medicines as prescribed, and let them know if you notice trouble.
Interaction: Additive antimuscarinic/GI-slowing and urinary effects when fentanyl (mu-opioid agonist) is combined with the anticholinergic trospium component of trospium/xanomeline (Cobenfy).
- Effect: Increased risk of urinary retention and severe constipation, potentially progressing to paralytic ileus.
- Mechanism: Unknown/pharmacodynamic additive reduction in GI motility and detrusor function; neither agent is metabolically driving the other here.
- Evidence: Theoretical. Severity: Major. Onset: Unspecified.
- Management: Monitor for reduced gastric motility, abdominal distension, and urinary retention. Encourage bowel regimen; individualize therapy and consider prophylactic laxatives.
What happens
Increased risk of urinary retention and/or severe constipation, which may lead to paralytic ileus
Interaction Deep Dive
When fentaNYL is given together with an anticholinergic agent, the combination may raise the likelihood of severe constipation or urinary retention, with the potential to progress to paralytic ileus. Watch patients for indications of decreased gastric motility or urinary retention123.
Why it happens (mechanism)
Unknown
How to manage this interaction
How your care team manages this:
- They will watch you for signs of urinary retention (trouble urinating) and reduced gut movement (severe constipation, bloating, no bowel movements).
- They may suggest a bowel routine or laxative support, and your doses may be adjusted and individualized as needed.
What you should do: Keep taking both medicines exactly as prescribed. Contact your pharmacist or prescriber promptly if you cannot pass urine, have belly swelling or pain, or go without a bowel movement for longer than usual. These are manageable when caught early.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Fentanyl and Trospium / Xanomeline together?
Taking fentanyl with trospium (Cobenfy) can add up to worse constipation and trouble urinating, so watch for those signs and call your pharmacist or doctor if they happen. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fentanyl and Trospium / Xanomeline 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 Fentanyl and Trospium / Xanomeline interaction managed?
How your care team manages this: They will watch you for signs of urinary retention (trouble urinating) and reduced gut movement (severe constipation, bloating, no bowel movements). They may suggest a bowel routine or laxative support, and your doses may be adjusted and individualized as needed. What you should do: Keep taking both medicines exactly as prescribed. Contact your pharmacist or prescr… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Fentanyl or Trospium / Xanomeline 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 (3)
- Product Information: FENTORA(R) buccal tablets, fentanyl citrate buccal tablets. Teva Pharmaceuticals USA Inc (per FDA), Parsippany, NJ, 2023.
- Product Information: Fentanyl citrate intravenous, intramuscular injection, fentanyl citrate intravenous, intramuscular injection. Hospira Inc (per FDA), Lake Forest, IL, 2023. DailyMed
- Product Information: ACTIQ(R) oral transmucosal lozenge, fentanyl citrate oral transmucosal lozenge. Teva Pharmaceuticals USA, Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
Keep reading about Fentanyl
Keep reading about Trospium / Xanomeline
These medications also interact with supplements
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist