Drug interactions
acetaminophen + warfarin
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Overview
Acetaminophen can potentiate warfarin, increasing INR and bleeding risk—especially at doses ≥2 g/day for several consecutive days.
Mechanism of action
Proposed: acetaminophen metabolite (NAPQI) interferes with the vitamin K cycle (e.g., inhibition/oxidation of vitamin K hydroquinone), enhancing anticoagulation; CYP-mediated effects are less likely.
Clinical management
Use the lowest effective acetaminophen dose; avoid ≥2 g/day for >3 days when possible. If regular use or dose increase occurs, check INR within 3–5 days and adjust warfarin as needed. Counsel on bleeding signs and review combo products containing acetaminophen.
Drug reference
References
- Warfarin (Coumadin) Prescribing Information — FDA Label
- Warfarin monograph — Lexicomp
Frequently asked questions
Can I take acetaminophen with warfarin?
The interaction is rated: Moderate. Acetaminophen can potentiate warfarin, increasing INR and bleeding risk—especially at doses ≥2 g/day for several consecutive days.
How serious is the interaction between acetaminophen and warfarin?
The interaction is rated: Moderate. Evidence level: High.
How is the interaction between acetaminophen and warfarin managed?
Use the lowest effective acetaminophen dose; avoid ≥2 g/day for >3 days when possible. If regular use or dose increase occurs, check INR within 3–5 days and adjust warfarin as needed. Counsel on bleeding signs and review combo products containing acetaminophen.
Why do acetaminophen and warfarin interact?
Proposed: acetaminophen metabolite (NAPQI) interferes with the vitamin K cycle (e.g., inhibition/oxidation of vitamin K hydroquinone), enhancing anticoagulation; CYP-mediated effects are less likely.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.