Acetaminophen And Codeine and Acenocoumarol: 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
Acenocoumarol
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.
The pain reliever you're taking contains acetaminophen (the same ingredient as Tylenol) plus codeine. Your other medicine, acenocoumarol, is a blood thinner. When you take acetaminophen regularly, it can make your blood thinner work a little stronger, which raises the chance of easier bruising or bleeding.
This isn't a reason to panic. Occasional or short-term use of acetaminophen is usually fine. The key is not to take large amounts every day for long stretches without letting your care team know. Your doctor can simply check your INR (the blood test that shows how thin your blood is) and adjust things if needed. Please talk with your pharmacist or doctor before changing anything.
Effect: Acetaminophen may potentiate the anticoagulant effect of acenocoumarol, increasing INR and bleeding risk.
- Mechanism: Probable inhibition of acenocoumarol metabolism and/or interference with vitamin K-dependent clotting factor synthesis. Neither agent's active anticoagulant depends on the other for activation.
- Direction/magnitude: Increased anticoagulant response; a case report showed INR falling from ~2.46 to 1.62 on acetaminophen withdrawal and rising again on rechallenge.
- Onset: Delayed. Evidence: Probable.
- Management: Acenocoumarol is a narrow-therapeutic-index agent. Limit acetaminophen to
What happens
Potentiation of anticoagulant effect
Interaction Deep Dive
The anticoagulant effect of acenocoumarol may be potentiated by acetaminophen administration. A 72-year-old male stabilized on acenocoumarol 2 mg daily began self-medicating with acetaminophen 1 to 2 grams daily for lower back pain. The consistency of acetaminophen dosing is not known, but his International Normalized Ratio (INR) values remained stable with an average INR of 2.46. Approximately two weeks after discontinuing acetaminophen, his INR decreased to 1.62. One week later the INR was 1.67. The patient restarted acetaminophen 1 g daily and his INR increased to 2.02 within a week1.
Why it happens (mechanism)
Inhibition of acenocoumarol metabolism or interference with clotting factor formation
How to manage this interaction
You can generally keep taking both as prescribed. The concern is mainly with regular, higher-dose acetaminophen use, not an occasional dose.
- A sensible limit is no more than 2 grams of acetaminophen per day, for only a few days.
- If you need larger amounts or need it for longer, your team may check your INR (prothrombin time) more closely and adjust your acenocoumarol dose, which is tailored to you.
- Watch for and report unusual bruising, nosebleeds, bleeding gums, or dark stools.
- Tell your pharmacist or doctor before starting, stopping, or changing how much acetaminophen you take.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Acetaminophen And Codeine and Acenocoumarol together?
Regular or higher-dose acetaminophen can strengthen acenocoumarol and raise bleeding risk, so keep acetaminophen to about 2 grams a day for only a few days, and ask your care team to check your INR if you need more. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Acetaminophen And Codeine and Acenocoumarol interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How is the Acetaminophen And Codeine and Acenocoumarol interaction managed?
You can generally keep taking both as prescribed. The concern is mainly with regular, higher-dose acetaminophen use, not an occasional dose. A sensible limit is no more than 2 grams of acetaminophen per day, for only a few days. If you need larger amounts or need it for longer, your team may check your INR (prothrombin time) more closely and adjust your acenocoumarol dose, which is tailored to you… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Acetaminophen And Codeine or Acenocoumarol 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 anything you'd monitor while I'm on both?
References (1)
- Bagheri H, Bernhard NB, & Montastruc JL: Potentiation of the acenocoumarol anticoagulant effect by acetaminophen (letter). Ann Pharmacother 1999; 33:506. PubMed
Keep reading about Acetaminophen And Codeine
Keep reading about Acenocoumarol
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major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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