Flavoxate 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
Flavoxate
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.
Your pain medicine contains codeine, which can slow down your gut and make it harder to have a bowel movement or empty your bladder. Flavoxate works by relaxing the bladder, and it can also slow the gut. Taken together, these two can add up and cause serious constipation or trouble urinating. In rare cases, the bowel can slow so much that it nearly stops (called a paralytic ileus).
This concern is based mostly on how the drugs work, not lots of real-world reports. Still, it is worth watching. Please keep taking both as prescribed and let your care team know if you notice belly pain, bloating, no bowel movements, or trouble peeing. They can manage this easily.
Effect: Additive risk of urinary retention and severe constipation, potentially progressing to paralytic ileus.
Mechanism: Pharmacodynamic additivity. Codeine, an opioid agonist, reduces GI motility and bladder tone; flavoxate has anticholinergic/antimuscarinic and smooth-muscle relaxant properties that further impair gastric motility and urinary emptying.
- Direction: Additive PD effect (not a PK/metabolism interaction).
- Onset: Unspecified.
- Evidence: Theoretical; severity rated major.
- Management: Monitor for reduced bowel sounds, abdominal distension, constipation, and urinary retention. Dose and use may be individualized by the care team; consider bowel regimen if opioid continued.
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
Good news: this is manageable, and you should keep taking both medicines as prescribed unless your prescriber tells you otherwise.
- Watch for warning signs: constipation, no bowel movement, bloating or belly pain, and trouble passing urine.
- Report any of these to your pharmacist or prescriber promptly.
- Your care team may monitor you more closely and can adjust and individualize your plan (for example, adding a stool softener or laxative regimen if needed).
- Stay hydrated and keep moving as you are able, which helps your gut stay active.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Flavoxate and Acetaminophen And Codeine together?
Codeine plus flavoxate can add up to cause serious constipation or trouble urinating, so watch for these signs and tell your care team; keep taking both as prescribed unless told otherwise. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Flavoxate 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 Flavoxate and Acetaminophen And Codeine interaction managed?
Good news: this is manageable, and you should keep taking both medicines as prescribed unless your prescriber tells you otherwise. Watch for warning signs: constipation, no bowel movement, bloating or belly pain, and trouble passing urine. Report any of these to your pharmacist or prescriber promptly. Your care team may monitor you more closely and can adjust and individualize your plan (for examp… 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 Flavoxate 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 Flavoxate
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