Acetaminophen And Codeine and Thioridazine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 1, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Acetaminophen And Codeine
Thioridazine
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.
Let's talk about taking your acetaminophen with codeine alongside thioridazine. Codeine is a "prodrug," which means your body has to turn it into morphine to give you pain relief. Thioridazine can speed up how quickly your body breaks codeine down, so you may get less pain relief, and if you've been on codeine a while you could even feel withdrawal.
At the same time, both medicines can slow your gut and calm your brain, so together they may cause bad constipation, trouble urinating, heavy drowsiness, or slowed breathing. This is worth watching, but your care team can manage it. Please talk with your doctor or pharmacist before changing anything.
Direction: Dual concern. Codeine is a prodrug requiring CYP2D6 activation to morphine.
- PK: Thioridazine (CYP3A4 induction) may shunt codeine toward norcodeine, lowering morphine formation, reducing analgesia, and risking withdrawal in dependent patients.
- PD: Additive anticholinergic and CNS depressant effects raise risk of urinary retention, severe constipation/paralytic ileus, sedation, respiratory depression, hypotension.
Evidence: Theoretical. Severity: major. Onset: unspecified.
Management: Reserve concurrent use for when alternatives are inadequate; use lowest effective dose and shortest duration. Monitor for reduced efficacy, withdrawal, constipation, retention, sedation, and respiratory depression. Consider prescribing naloxone.
What happens
Reduced codeine and morphine exposure, increased risk of paralytic ileus and an increased risk of respiratory and CNS depression
Interaction Deep Dive
Limit combining codeine with anticholinergic CNS depressants to those patients for whom other options are insufficient. When such combined use cannot be avoided, employ the smallest dose over the briefest period needed to reach therapeutic objectives. Giving codeine together with anticholinergic CNS depressants can heighten the likelihood of urinary retention and/or severe constipation, potentially progressing to paralytic ileus, respiratory depression, hypotension, sedation, coma, or death. Furthermore, using codeine alongside CYP3A4 inducers may lower codeine concentrations, raise norcodeine concentrations, and reduce CYP2D6-mediated metabolism, thereby producing lower morphine concentrations and leading to diminished effectiveness or the emergence of a withdrawal syndrome in patients who have become physically dependent. Should combined use be required, monitor patients carefully for reduced efficacy or indications of opioid withdrawal syndrome, urinary retention, severe constipation, sedation, and respiratory depression. When such combined use is justified, consider prescribing naloxone for the emergency management of opioid overdose12.
Why it happens (mechanism)
Induction of CYP3A4-mediated codeine metabolism; additive effects on gastric motility; additive CNS depression
How to manage this interaction
If both medicines are prescribed together, keep taking them as directed. Your care team can manage this by tailoring the dose and watching you more closely.
- Your team may use the lowest dose for the shortest time needed, and the codeine dose may be adjusted and individualized.
- They may monitor for weaker pain control or withdrawal signs (restlessness, sweating, cramps), plus severe constipation, trouble urinating, heavy drowsiness, or slowed breathing.
- They may discuss having naloxone on hand as a safety measure.
Call your pharmacist or prescriber before stopping or changing either drug, and get urgent help for very slow breathing or extreme sedation.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) Observational research has shown that using opioid analgesics together with benzodiazepines raises the likelihood of drug-related death when compared with opioid analgesic use by itself. Given their comparable pharmacological characteristics, it is reasonable to anticipate a similar risk when other CNS depressant drugs are used alongside opioid analgesics 12.
Common questions
Can I take Acetaminophen And Codeine and Thioridazine together?
Thioridazine may lower codeine's pain relief while adding to constipation, drowsiness, and slowed breathing risk; keep taking both as prescribed and ask your care team about dose and monitoring. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Thioridazine 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 Thioridazine interaction managed?
If both medicines are prescribed together, keep taking them as directed. Your care team can manage this by tailoring the dose and watching you more closely. Your team may use the lowest dose for the shortest time needed, and the codeine dose may be adjusted and individualized. They may monitor for weaker pain control or withdrawal signs (restlessness, sweating, cramps), plus severe constipation, t… 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 Thioridazine 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 (2)
- Product Information: Codeine sulfate oral solution, codeine sulfate oral solution. Hikma Pharmaceuticals USA Inc(per FDA), Berkeley Heights, NJ, 2023. DailyMed
- Product Information: Codeine sulfate oral tablets, codeine sulfate oral tablets. Hikma Pharmaceuticals USA Inc. (per FDA), Berkeley Heights, NJ, 2023. DailyMed
Keep reading about Acetaminophen And Codeine
Keep reading about Thioridazine
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist