Supplements and Warfarin

Vitamin K directly counteracts warfarin. Warfarin works by blocking vitamin K. Starting, stopping or changing vitamin K intake can shift your INR and clotting risk. Don't change it without your prescriber.

St. John's wort weakens warfarin. It speeds up the breakdown of warfarin, which can lower your INR and lead to clots. Do not combine without your prescriber.

Glucosamine can raise INR on warfarin. Case reports and FDA and WHO adverse-event reports describe higher INR and bleeding in people on warfarin who took glucosamine, often after increasing the dose. Don't start, stop or change glucosamine without your prescriber, and get your INR checked.

Multivitamins may contain vitamin K. NIH advises people on warfarin to talk with their health care provider before taking any multivitamin that contains vitamin K, because vitamin K lowers warfarin's effect. Keep your intake consistent and check the label.

CoQ10 may make warfarin less effective. CoQ10 is structurally similar to vitamin K, and case reports describe a lower INR. Tell your prescriber before starting or stopping it.

High-dose omega-3 may add to bleeding risk. Doses above ~3 g/day EPA+DHA can prolong bleeding time. The clinical significance with blood thinners is debated; let your prescriber know.

Curcumin may increase bleeding risk. Curcumin has antiplatelet effects, and case reports describe a raised INR in people on warfarin.

Resveratrol may inhibit platelets. Resveratrol inhibits platelet aggregation in lab studies, which could add to the effect of blood thinners.

Ginkgo may increase bleeding risk. Ginkgo may add to the effect of blood thinners such as warfarin.

High-dose vitamin E may add to bleeding risk. Vitamin E can inhibit platelets and antagonize vitamin K, especially above ~400 IU/day.

Piperine can raise drug levels. Piperine inhibits CYP3A4 and P-glycoprotein, which clear many medications, including some blood thinners. Ask your pharmacist.

Berberine can change drug levels. Berberine inhibits several drug-metabolizing enzymes (CYP2D6, CYP3A4, CYP2C9). Ask your pharmacist.

Nattokinase adds to bleeding risk. It breaks down fibrin, and a brain bleed was reported in a patient taking it with aspirin. Don't combine with blood thinners without your prescriber.

Garlic supplements may increase bleeding risk. NIH notes that garlic supplements may increase the risk of bleeding, especially with anticoagulants or aspirin. Tell your prescriber.

Fisetin has antiplatelet activity in animal studies. Theoretical additive bleeding risk; human data are lacking.

Ginger's effect on bleeding is uncertain. Studies disagree on whether ginger reduces platelet clumping. Normal food amounts are fine; mention supplements to your prescriber.