Atropine 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
Atropine
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 can slow down your gut and make it harder to pee. Codeine (the pain part of your acetaminophen and codeine) commonly causes constipation. Atropine is an anticholinergic, which means it also slows the bowels and the bladder. Put together, they can push those effects further, and in rare cases the gut can slow so much that it nearly stops, which is called a paralytic ileus.
Watch for hard, infrequent stools, a swollen or painful belly, or trouble urinating. This concern is mostly theoretical, and your care team can manage it by keeping an eye on you. Please talk with your pharmacist or doctor before making any changes.
Effect: Additive slowing of GI motility and urinary function, with a theoretical increased risk of severe constipation, urinary retention, and paralytic ileus.
Mechanism: Codeine (opioid) reduces gut motility; atropine (antimuscarinic) adds anticholinergic effects on smooth muscle and bladder. Pharmacodynamic, additive.
- Direction: Additive PD effect, not a PK/enzyme interaction.
- Evidence: Theoretical; severity rated major.
- Onset: Unspecified.
- Management: Monitor for reduced bowel sounds, abdominal distension, constipation, and urinary retention. Consider prophylactic bowel regimen and individualized dosing per care team.
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 medicines exactly as prescribed unless your care team tells you otherwise. Because both can slow the gut and bladder, your team may watch you more closely and tailor your treatment.
- Tell your prescriber or pharmacist about constipation, a swollen or painful belly, nausea/vomiting, or trouble urinating.
- Ask whether stool softeners, fluids, and fiber may help prevent constipation.
- Your doses may need to be adjusted and individualized by your care team.
- Seek prompt care if your belly becomes very hard, bloated, and painful, or you cannot pass stool or urine.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Atropine and Acetaminophen And Codeine together?
Combining codeine with atropine can add up to worsen constipation and urinary retention, and rarely a stalled bowel (paralytic ileus). Keep taking both as prescribed, watch for these symptoms, and check with your pharmacist or doctor. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Atropine 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 Atropine and Acetaminophen And Codeine interaction managed?
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Because both can slow the gut and bladder, your team may watch you more closely and tailor your treatment. Tell your prescriber or pharmacist about constipation, a swollen or painful belly, nausea/vomiting, or trouble urinating. Ask whether stool softeners, fluids, and fiber may help prevent constipation. Y… 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 Atropine 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 Atropine
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