Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
Warfarin is an anticoagulant, often called a blood thinner: it blocks vitamin K from doing its part in making clotting factors, so blood takes longer to clot. It is used to prevent and treat clots in the legs and lungs, to lower the chance of stroke in atrial fibrillation, and after a mechanical heart valve is fitted. Its effect is checked with a blood test (the INR). It is sold as Coumadin and Jantoven, among other names.
Two genes explain much of why people need very different amounts of warfarin. VKORC1 makes the enzyme warfarin blocks, and a common variant (rs9923231) makes less of it, so less warfarin has the same effect. CYP2C9 breaks warfarin down, and its *2 and *3 variants slow that, so it stays in the body longer. CYP4F2 plays a smaller part. CPIC and DPWG have published guidelines on these genes and warfarin, and the US drug label includes a table based on CYP2C9 and VKORC1. Hundreds of studies have looked at these and other genes.
Clinical guidelines that name a gene for Warfarin. They sort people into groups by the gene copies they carry.
DPWG guideline: VKORC1. rs9923231 C/C · rs9923231 C/T · rs9923231 T/T.
Every published finding on gene variants and Warfarin. Upload your DNA file to see which of these rows apply to you.
PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.
CYP2C9 CYP2C9*1, CYP2C9*2, CYP2C9*3, CYP2C9*4, CYP2C9*5, CYP2C9*6, CYP2C9*8, CYP2C9*11: Level 1A · replicated. Dosage: Cardiovascular Disease. 130.
VKORC1 rs9923231: Level 1A · replicated. Dosage. 86.
CYP4F2 rs2108622: Level 1A · replicated. Dosage. 69.
CYP2C9 CYP2C9*1, CYP2C9*2, CYP2C9*3, CYP2C9*5, CYP2C9*6, CYP2C9*11: Level 1A · replicated. Toxicity: Hemorrhage. 33.
Studies of how quickly the body processes this medication.
Studies of how well it worked in people carrying a variant.
Studies of how much of the drug people needed or tolerated.
rs12772169: Allele T is associated with dose of warfarin as compared to allele C.
rs12777823: Allele A is associated with dose of warfarin as compared to allele G.
Studies that do not fall into the groups above.
EPHX1 rs2234922: Allele G is not associated with dose of warfarin.
ORM1, ORM2 rs1687390: Allele G is not associated with dose of warfarin.
Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.
More drugs from the same category
Acenocoumarol (Anticoagulants)
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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