Allopurinol and Warfarin Interaction
Drug interaction information between Allopurinol and Warfarin.
Allopurinol and Warfarin have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Allopurinol and Warfarin. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
How They Interact
Allopurinol slows down the body's ability to break down warfarin. This can cause warfarin to stay in the body longer and increase the risk of bleeding.
FDA Label Information
Warfarin Clinical Impact Allopurinol may inhibit the metabolism of warfarin, possibly enhancing its anticoagulant effect. Assess INR frequently and adjust warfarin dosage accordingly when allopurinol is added to warfarin therapy.
Allopurinol Also Interacts With
- Pegloticase major
- Cyclosporine moderate
- Amoxicillin moderate
- Amoxicillin/Clavulanate moderate
- Theophylline minor
Warfarin Also Interacts With
- Fluoxetine major
- Tamoxifen major
- Ibuprofen moderate
- Aspirin moderate
- Diclofenac moderate
Frequently Asked Questions
What SPL severity band is on file for Allopurinol + Warfarin?
Compiled FDA labeling labels this pair minor. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Warfarin has 163 labeled pairs on file vs Allopurinol's 10. In the minor band specifically: Allopurinol has 6 (also Theophylline, Ampicillin/Sulbactam, Famciclovir, Prazosin); Warfarin has 133 (also Atorvastatin, Amlodipine, Omeprazole, Famotidine).
What mechanism field is on file for Allopurinol and Warfarin?
Allopurinol slows down the body's ability to break down warfarin. This can cause warfarin to stay in the body longer and increase the risk of bleeding.
Warfarin carries more major-labeled pairs than Allopurinol
SPL source-record counts only. This page's band is minor · classes on file: Allopurinol (Xanthine Oxidase Inhibitor); Warfarin (Vitamin K Antagonist (Anticoagulant)).
Warfarin has 2 major-labeled pairs vs Allopurinol's 1. This page itself is in the minor band, not the major band.
1 major · 3 moderate · 6 minor · 10 total
- Other minor peers for Allopurinol
- Theophylline
- Ampicillin/Sulbactam
- Famciclovir
- Prazosin
2 major · 28 moderate · 133 minor · 163 total
- Other minor peers for Warfarin
- Atorvastatin
- Amlodipine
- Omeprazole
- Famotidine
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.