Can You Take Aspirin with Warfarin?
Last reviewed: · Source: US FDA drug label database
Avoid — aspirin significantly increases bleeding risk when taken with warfarin and can cause serious haemorrhage.
Is it safe to take Aspirin with Warfarin?
Taking aspirin with warfarin greatly increases your risk of serious bleeding, including internal bleeding, stomach bleeds, and brain haemorrhage. Aspirin affects platelets (which help blood clot) while warfarin affects clotting factors. Together, they can impair your blood's ability to clot from two different directions, making bleeds much harder to stop. This combination should only be used under explicit medical supervision for specific conditions (such as mechanical heart valves) where the benefit outweighs the risk.
How do Aspirin and Warfarin interact?
Warfarin inhibits vitamin K-dependent clotting factors (II, VII, IX, X) via VKORC1 enzyme blockade, prolonging INR. Aspirin irreversibly inhibits COX-1 in platelets, impairing platelet aggregation. Aspirin also has a direct irritant effect on the stomach lining, increasing GI bleed risk. Additionally, higher doses of aspirin can displace warfarin from plasma protein binding, raising free warfarin levels and increasing its anticoagulant effect unpredictably.
Data sourced from the US Food and Drug Administration (FDA) drug label database: FDA warfarin drug label — interaction section; OpenFDA drug label data.
Who should be careful?
Everyone taking warfarin must be careful with aspirin. If your doctor has specifically prescribed both (rare but sometimes done for mechanical heart valves), your INR will need very close monitoring. Never start or stop aspirin without telling your anticoagulation clinic.
What if I've already taken Aspirin and Warfarin?
If you have taken both together without medical advice, contact your GP or pharmacist immediately. Watch for signs of bleeding: unusual bruising, blood in urine or stools (black or red), prolonged bleeding from cuts, or unusual headaches. In an emergency, call 999.
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Frequently Asked Questions
Can I take aspirin with warfarin?
Generally no. This combination significantly increases bleeding risk. You should only take aspirin if your doctor has specifically told you to, and your INR must be closely monitored.
What can I take for pain instead of aspirin if I am on warfarin?
Paracetamol is the safest painkiller to use with warfarin, though even paracetamol can slightly increase INR at higher doses. Avoid all NSAIDs (ibuprofen, aspirin, naproxen) without medical advice.
Why do some people take both aspirin and warfarin?
In rare cases, doctors prescribe both for patients with mechanical heart valves or very high-risk cardiovascular disease, where the clot-prevention benefit outweighs the increased bleeding risk. This requires strict medical supervision.
Does aspirin affect my INR?
Aspirin does not directly affect INR, but it can displace warfarin from proteins in the blood at high doses, which may raise effective warfarin levels. The bigger concern is the combined effect on bleeding from two different pathways.