Warfarin and Cholestyramine Resin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Cholestyramine Resin
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 effects of warfarin
Interaction Deep Dive
Cholestyramine has been shown to decrease the absorption and may interrupt the enterohepatic recirculation of warfarin, phenprocoumon, and dicumarol resulting in a reduced anticoagulant effect21456.
Why it happens (mechanism)
Decreased warfarin absorption, interference with enterohepatic recirculation
Literature reports
1 report — tap to read
a) Six healthy subjects were studied to determine the significance of cholestyramine interaction with warfarin 3. Cholestyramine 12 g (administered in 3 divided doses) was added to warfarin 40 mg. The interaction was tested in two ways: 1) cholestyramine 4 g was given concomitantly with the warfarin dose and the other 2 cholestyramine doses at successive 3 hour intervals, and 2) cholestyramine 4 g was given 3 hours before the warfarin dose and 3 and 6 hours after the warfarin dose. It was noted that cholestyramine significantly (p greater than 0.01) decreased plasma warfarin concentration for both concomitant and remote administration when compared to control values. It was postulated that little binding of warfarin by cholestyramine occurs in the acid stomach, but, when warfarin enters the small bowel, it is converted to its anionic form which would promote binding, thereby making it unavailable for absorption 3.
Common questions
Can I take Warfarin and Cholestyramine Resin together?
Decreased effects of warfarin Always confirm with your pharmacist or prescriber before making any change.
How serious is the Warfarin and Cholestyramine Resin 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 Warfarin or Cholestyramine Resin 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 (6)
- Jahnchen E, Meinertz T, Gilfrich HJ, et al: Enhanced elimination of warfarin during treatment with cholestyramine. Br J Clin Pharmacol 1978; 5:437-440. DOI
- Meinertz T, Gilfrich MJ, Bork R, et al: Treatment of phenprocoumon intoxication with cholestyramine. Br Med J 1977; 2:439. PubMed
- Robinson DS, Benjamin DM, & McCormick JJ: Interaction of warfarin and nonsystemic gastrointestinal drugs. Clin Pharmacol Ther 1971; 12:491-495. PubMed
- Koch-Weser J & Koch-Weser J: Drug interactions in cardiovascular therapy. Am Heart J 1975; 90:93-116. DOI
- Koch-Weser J & Sellers EM: Drug interactions with coumarin anticoagulants (part 2). N Engl J Med 1971; 285:547-558. DOI
- Harvengt C & Desager JP: Effect of colestipol, a new bile acid sequestrant, on the absorption of phenprocoumon in man. Eur J Clin Pharmacol 1973; 6:19-21. DOI
Keep reading about Warfarin
Keep reading about Cholestyramine Resin
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