Fesoterodine 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
Fesoterodine
Trospium / 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.
Both of these medicines work by blocking a body signal called acetylcholine. Fesoterodine (Toviaz) calms an overactive bladder, and the trospium part of Cobenfy works the same way. When you take two medicines that do the same thing, their side effects can add up.
That means you might notice more dry mouth, constipation, blurry vision, trouble emptying your bladder, or feeling overheated. This concern is based on how the drugs work rather than strong studies, so it may not happen to you. The good news is your care team can watch for these effects and adjust things if needed. Keep taking both as prescribed and let your pharmacist or doctor know if the dryness or constipation bothers you.
Mechanism: Additive antimuscarinic (anticholinergic) pharmacodynamic effect. Fesoterodine is a competitive muscarinic antagonist (active metabolite 5-HMT); trospium is also a muscarinic antagonist. Neither drug's activation is the concern here, so this is a PD, not PK, interaction.
Direction: Additive antimuscarinic burden, increasing frequency/severity of anticholinergic adverse effects (xerostomia, constipation, urinary retention, blurred vision, cognitive effects in the elderly, impaired thermoregulation).
- Onset: unspecified
- Evidence: theoretical
- Management: monitor for increased anticholinergic effects; dose may be individualized by the prescriber; consider avoiding duplicate antimuscarinic therapy where clinically appropriate.
What happens
An increased risk of anticholinergic adverse reactions (eg, dry mouth, constipation)
Interaction Deep Dive
Taking trospium/xanomeline together with other antimuscarinic agents known to cause anticholinergic adverse reactions (for instance, dry mouth or constipation) can heighten how often and/or how severely these reactions occur. When these drugs are used together, patients should be watched for a rise in the frequency and/or intensity of anticholinergic adverse reactions1.
Why it happens (mechanism)
Additive antimuscarinic effects
How to manage this interaction
Your care team can manage this by watching how you feel and tailoring your treatment.
- Keep taking both exactly as prescribed unless your doctor tells you otherwise.
- Watch for and report dry mouth, constipation, blurred vision, trouble urinating, or feeling overheated.
- Your prescriber may monitor you more closely, and your doses may be adjusted and individualized to lower the combined effect.
- Because two bladder-type antimuscarinic drugs overlap, ask your pharmacist whether both are truly needed for you.
Simple steps like sipping water, sugar-free gum, and fiber or fluids can ease dryness and constipation. Raise any bothersome symptoms with your pharmacist or doctor.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Fesoterodine and Trospium / Xanomeline together?
Taking Fesoterodine with trospium/xanomeline can add up their anticholinergic side effects like dry mouth and constipation, so keep taking both as prescribed and tell your care team about any bothersome symptoms. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Fesoterodine and Trospium / Xanomeline interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Fesoterodine and Trospium / Xanomeline interaction managed?
Your care team can manage this by watching how you feel and tailoring your treatment. Keep taking both exactly as prescribed unless your doctor tells you otherwise. Watch for and report dry mouth, constipation, blurred vision, trouble urinating, or feeling overheated. Your prescriber may monitor you more closely, and your doses may be adjusted and individualized to lower the combined effect. Becau… 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 Fesoterodine 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 anything you'd monitor while I'm on both?
References (1)
- Citation #1
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Keep reading about Trospium / Xanomeline
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