Colesevelam and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Colesevelam
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
Reduced INR results
Interaction Deep Dive
Postmarketing cases of decreased INR have been reported among patients receiving warfarin and colesevelam concomitantly. If co-treatment with colesevelam and warfarin is necessary, patients should take warfarin at least 4 hours prior to colesevelam. Alternatively, patients should be monitored for an adequate response to warfarin therapy and the warfarin dose should be adjusted appropriately. INR should be monitored prior to colesevelam initiation, frequently during concomitant therapy with colesevelam therapy, and, once INR is stable, periodically thereafter1.
Why it happens (mechanism)
Reduced absorption of warfarin by nonspecific binding with colesevelam
Literature reports
1 report — tap to read
a) Reduced INR was reported in patients receiving warfarin and colesevelam concomitantly during postmarketing use; frequency and causality have not been established. However, there was no significant alteration of warfarin drug levels with coadministration of colesevelam in an in vivo pharmacokinetics study 1.
Common questions
Can I take Colesevelam and Warfarin together?
Reduced INR results Always confirm with your pharmacist or prescriber before making any change.
How serious is the Colesevelam and Warfarin interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
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 Colesevelam 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)
- Product Information: WELCHOL oral tablets, colesevelam hcl oral tablets. Daiichi Sankyo Inc, Parsippany, NJ, 2008. DailyMed
Keep reading about Warfarin
Keep reading about Colesevelam
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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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