Acetaminophen And Codeine and Hyoscyamine: 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
Hyoscyamine
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, and one of its common side effects is slowing down your gut and making it harder to pee. Hyoscyamine works differently, but it also slows the gut and the bladder. When you take both, those effects can add up.
In some cases this can cause bad constipation or trouble emptying your bladder. Rarely, the gut can slow down so much it nearly stops (called paralytic ileus). This is a theoretical concern, not something that happens to everyone, but it is worth knowing. Keep taking both as prescribed, drink fluids, stay active if you can, and tell your doctor or pharmacist if you notice belly bloating, no bowel movements, or trouble urinating. Your care team can manage this.
Effect: Additive anticholinergic and opioid effects on GI and urinary smooth muscle, increasing risk of severe constipation, urinary retention, and potentially paralytic ileus.
Mechanism: Codeine reduces GI motility via mu-opioid receptors; hyoscyamine is an antimuscarinic that further inhibits gut and bladder motility. Effects are additive, not metabolic. Neither activation nor prodrug status alters the direction here.
Evidence: Theoretical. Onset: unspecified. Severity: major.
- Monitor for reduced bowel sounds, abdominal distension, absent stool, and urinary retention.
- Encourage hydration, mobility, and consider a bowel regimen.
- Adjust dosing or consider alternatives if symptoms emerge.
What happens
An increased risk of paralytic ileus
Interaction Deep Dive
When codeine is taken together with anticholinergic agents, the likelihood of urinary retention and/or severe constipation may rise, and this can progress to paralytic ileus. In patients receiving codeine alongside anticholinergic drugs, watch for indications of urinary retention or diminished gastric motility1.
Why it happens (mechanism)
Additive effects on gastric motility
How to manage this interaction
Both medicines can slow your gut and bladder, so together they raise the chance of constipation or trouble urinating. This is usually manageable.
- Keep taking both as prescribed unless your prescriber tells you otherwise.
- Watch for no bowel movements, belly bloating or pain, or trouble passing urine.
- Stay well hydrated and keep moving when possible; ask about a stool softener if constipation starts.
- Report symptoms early. Your care team may adjust doses, individualize your regimen, or monitor you more closely.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Hyoscyamine together?
Taking codeine with hyoscyamine can add up to cause serious constipation or urinary retention, so watch for these and report them promptly. Your care team can adjust and monitor to keep you safe. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Hyoscyamine 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 Hyoscyamine interaction managed?
Both medicines can slow your gut and bladder, so together they raise the chance of constipation or trouble urinating. This is usually manageable. Keep taking both as prescribed unless your prescriber tells you otherwise. Watch for no bowel movements, belly bloating or pain, or trouble passing urine. Stay well hydrated and keep moving when possible; ask about a stool softener if constipation starts… 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 Hyoscyamine 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 Hyoscyamine
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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