Acetaminophen And Codeine and Biperiden: 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
Biperiden
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.
You've been prescribed acetaminophen with codeine (a pain reliever) along with biperiden (used for movement problems). Both of these can slow down your gut and make you constipated, and codeine can also make it harder to empty your bladder. When you take them together, those effects can add up.
In rare cases, the gut can slow down so much that it nearly stops, which is called a paralytic ileus. This is a theoretical concern based on how the drugs work, not something that happens to most people. Watch for trouble having a bowel movement, belly pain or bloating, or trouble urinating, and let your care team know. They can manage this safely.
Effect: Additive reduction in GI motility and anticholinergic burden, raising the theoretical risk of severe constipation, urinary retention, and paralytic ileus.
Mechanism: Codeine (an opioid) slows gastric and intestinal motility; biperiden is an anticholinergic that further inhibits smooth muscle activity and bladder emptying. Effects are pharmacodynamic and additive, not PK-based.
- Direction: increased adverse GI/GU effect
- Onset: unspecified
- Evidence: theoretical
- Severity: major
Management: Monitor bowel function and urinary output. Consider prophylactic bowel regimen, ensure hydration, and individualize dosing. Escalate for abdominal distension, absent bowel sounds, or retention.
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
Keep taking both medications exactly as prescribed unless your care team tells you otherwise. The main goal here is to watch your gut and bladder.
- Watch for severe constipation, belly bloating or pain, no bowel movements, or trouble urinating, and report these promptly.
- Your team may monitor you more closely and can recommend steps to keep things moving, such as staying hydrated and using a stool softener or laxative if appropriate.
- Doses may be adjusted and individualized by your care team if needed.
Ask your pharmacist or prescriber before adding any other medicine that can cause constipation.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Biperiden together?
Taking codeine with biperiden can add up to cause serious constipation and difficulty urinating, which in rare cases can nearly stop the gut. Keep both as prescribed and tell your care team if you have belly bloating, no bowel movements, or trouble peeing. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Biperiden 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 Biperiden interaction managed?
Keep taking both medications exactly as prescribed unless your care team tells you otherwise. The main goal here is to watch your gut and bladder. Watch for severe constipation, belly bloating or pain, no bowel movements, or trouble urinating, and report these promptly. Your team may monitor you more closely and can recommend steps to keep things moving, such as staying hydrated and using a stool… 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 Biperiden 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 Biperiden
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