The right drug at the right dose at the right time

This section provides information only about this specific pharmacogenomic test.


  • If you have medication questions, ask your health care provider.
  • Follow your health care provider's instructions when taking any medication.
  • Do not change your medications without talking with your health care provider.

CYP2C9 & VKORC1/Warfarin Pharmacogenomic Lab Test

Key Facts

  • The CYP2C9/VKORC1 genetic test is used to predict how you will respond to a "blood thinner" medication called warfarin (Coumadin, Jantoven).
  • This test can help your health care provider to decide on the best starting dose of warfarin for you.
  • Your health care provider should continue to monitor you and adjust your dose as needed.
  • Your health care provider evaluates your test results and uses this information, along with your other health information, to make recommendations for appropriate treatment options.
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What should I do with my test results?

Talk to your health care provider or pharmacist about the results. They may suggest that you:

  • Keep taking a medication
  • Change the dose of a medication
  • Stop taking a medication
  • Take a different medication

What does my CYP2C9/VKORC1 result mean?

This test combines the impact of two genes that determines your sensitivity to the drug warfarin. Depending on the degree of warfarin sensitivity reported in your laboratory results, your health care provider may adjust your warfarin dose when you are starting therapy.

Who will see my results?

Only health care professionals, and those you have given permission, may view your genetic test results. If you are receiving care at another medical facility, we suggest you share this information with your other healthcare providers.

How could the CYP2C9 and VKORC1 test result affect my treatment with warfarin?

This test can help your healthcare provider to decide on the best starting dose of warfarin for you. Your healthcare provider should continue to monitor you and adjust your dose as needed.

Who is affected? Do different populations respond differently?

There is initial evidence that differences in ethnic populations may have different metabolic effects with warfarin.

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What is warfarin?

Warfarin (Coumadin, Jantoven), sometimes called a "blood thinner", is a medication used to treat or prevent blood clots. It is most often used for those at risk of deep vein thrombosis (DVT), pulmonary embolism (PE), and stroke.

Which gene affects my response to warfarin?

Variants in two different genes, CYP2C9 and VKORC1, influence the way your body processes (metabolizes) warfarin and can affect your response to this medication.

What problems can patients with the CYP2C9 and VKORC1 variants have when taking warfarin?

Certain variations in the CYP2C9 and VKORC1 genes can make individuals more or less sensitive to the blood-thinning effect of warfarin. Depending on the variant present, the person tested may need a lower or higher dose of warfarin.

Where can I find more information about warfarin and pharmacogenomics?

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These resources may help you understand more about individualized medicine, genomics and drug-gene testing (pharmacogenomics):

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If you have questions about your test results, ask to speak with your health care provider at your Mayo Clinic care location:

  • Minnesota
  • Arizona
  • Florida
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