Mesalamine Rectal and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Mesalamine Rectal
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.
What happens
Decreased warfarin efficacy
Interaction Deep Dive
The addition of mesalamine therapy to a stable regimen of warfarin resulted in a lack of a hypoprothrombinemic effect which caused a deep vein thrombosis in a 51-year-old female. Serum warfarin concentrations were not detectable. Although the mechanism is not known, possible causes include mesalamine inhibiting or preventing the absorption of warfarin1.
Why it happens (mechanism)
Unknown
Literature reports
1 report — tap to read
a) Warfarin 5 mg daily was being administered to a 51-year-old morbidly obese female with an international normalized ratio (INR) maintained between 2 and 3. Four weeks after she was prescribed mesalamine 800 mg three times daily, she presented with left leg pain and erythema of one day's duration. Lab values included prothrombin time (PT) of 11.3 seconds, partial thromboplastin time (PTT) of 23 seconds, and an INR of 0.9. Intravenous heparin therapy was initiated and titrated to a PTT of 50 seconds to 80 seconds. Warfarin was also continued, and an INR of 1.7 was achieved in six days. However, the INR again began to decrease despite increasing doses of warfarin. Serum warfarin concentrations were undetectable. Since mesalamine was the only new drug added to this patient's regimen prior to hospitalization, it was discontinued. The next day the INR was 1.8 and increased to 2.1 the following day 1.
Common questions
Can I take Mesalamine Rectal and Warfarin together?
Decreased warfarin efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Mesalamine Rectal and Warfarin 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 strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Mesalamine Rectal or Warfarin 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)
- Marinella MA: Mesalamine and warfarin therapy resulting in decreased warfarin effect (letter). Ann Pharmacother 1998; 32:841-842. PubMed
Keep reading about Warfarin
Keep reading about Mesalamine Rectal
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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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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