Many things influence how well a medication can work for you — including your genes. 

The US Food and Drug Administration (FDA) warns that up to 30% of people may have an adverse response to warfarin (brand name Coumadin®). Warfarin is the most commonly prescribed anticoagulant, or "blood thinner". How much warfarin is needed to prevent abnormal blood clots can vary greatly from person to person, because many things influence how we metabolize warfarin — age, weight, other medications, diet, and even ethnicity (race). Genes are a big factor, too.

Finding the right dose of warfarin can be difficult. Too much warfarin may lead to spontaneous bleeding, too little may lead to abnormal blood clots. Warfarin is the second most common drug that sends people to the emergency room, and 1 in 10 hospital admissions is the result of warfarin side effects.

Know your genetic "profile" — find the safest and most effective dose for you.

Common variations in two genes — called VKORC1 and CYP2C9 — explain about 40% of the variability in how people respond to warfarin. Knowing your genetic make-up for these two genes can help your doctor determine the safest and most effective warfarin dose for you.

FDA Changes Warfarin Label

The FDA has recognized that genetic factors are important to consider in warfarin dosing, and has highlighted studies showing that people with certain genetic markers respond differently. The FDA recommends that these genetic markers be considered when determining a warfarin dose, and recently added this information in the warfarin (generic) and Coumadin (brand name) product labels to highlight the testing and its use in determining a warfarin dose.