Acetaminophen And Codeine and Tolterodine: 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
Tolterodine
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.
You've been prescribed acetaminophen with codeine (a pain reliever) along with tolterodine (Detrol, used for an overactive bladder). Here's the thing to know: both of these can slow down your gut and make it harder to pee. Codeine, like other opioids, causes constipation, and tolterodine relaxes the bladder and slows the digestive tract too. Put together, they can add up.
The main worry is severe constipation or trouble urinating. In rare cases, the gut can slow so much it nearly stops, which is called a paralytic ileus. This is a theoretical concern, not something guaranteed to happen. Your care team can manage it easily by keeping an eye on things, so keep taking both as prescribed and tell them if you notice problems.
Effect: Additive risk of urinary retention, severe constipation, and potentially paralytic ileus when codeine (an opioid, itself a CYP2D6-activated prodrug for morphine) is combined with tolterodine (an antimuscarinic/anticholinergic).
Mechanism: Pharmacodynamic (additive), not PK. Opioid-induced reduction in GI motility plus anticholinergic slowing of gut motility and bladder emptying.
- Direction: Increased GI/urinary adverse effects
- Onset: Unspecified
- Evidence: Theoretical
- Severity: Major
Management: Monitor for reduced gastric motility, abdominal distension, and urinary retention. Consider prophylactic bowel regimen; individualize therapy and reassess if symptoms emerge.
What happens
An increased risk of paralytic ileus
Interaction Deep Dive
Taking codeine together with anticholinergic agents can raise the likelihood of urinary retention and/or severe constipation, potentially progressing to paralytic ileus. When codeine and anticholinergic agents are given at the same time, watch patients for indications of reduced gastric motility or urinary retention1.
Why it happens (mechanism)
Additive effects on gastric motility
How to manage this interaction
Good news: this is a manageable combination, and it's usually fine to keep taking both exactly as prescribed unless your prescriber tells you otherwise.
Here's what your care team may do and what you can do:
- Watch for warning signs: worsening constipation, no bowel movement for a few days, belly bloating or pain, or trouble urinating.
- Support your gut: your team may suggest ways to keep you regular (fluids, fiber, or a stool softener/laxative if appropriate for you).
- Closer monitoring: doses may be adjusted and individualized by your care team, and they may check in with you more often.
Call your pharmacist or doctor promptly if you notice these symptoms, and go for urgent care if you have severe belly pain or vomiting.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Tolterodine together?
Combining acetaminophen/codeine with tolterodine can add up to cause constipation or trouble urinating, and rarely a severely slowed gut. Keep taking both as prescribed, watch for these symptoms, and let your pharmacist or doctor know if they occur. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Tolterodine 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 Tolterodine interaction managed?
Good news: this is a manageable combination, and it's usually fine to keep taking both exactly as prescribed unless your prescriber tells you otherwise. Here's what your care team may do and what you can do: Watch for warning signs: worsening constipation, no bowel movement for a few days, belly bloating or pain, or trouble urinating. Support your gut: your team may suggest ways to keep you regula… 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 Tolterodine 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 Tolterodine
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.
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