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.

CYP2D6/Tamoxifen Pharmacogenomic Lab Test

Key Facts

  • The CYP2D6 genetic test is used to predict how you will respond to a large number of different medications.
  • You only need to have CYP2D6 genetic testing one time.
  • Your CYP2D6 result may have different recommendations based on the specific medications you are prescribed.
  • This website also provides information on the CYP2D6/tramadol and CYP2D6/codeine pharmacogenomic tests.
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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 CYP2D6 result mean if I'm taking tamoxifen?

Poor Metabolizer / Poor to Intermediate Metabolizer / Intermediate Metabolizer

Your body processes (metabolizes) tamoxifen more slowly to the more active form your body can use. Recommendations vary based on different types of breast cancer, the medications you are currently taking and your response to these medications. Talk with your healthcare provider about choosing a medication that may be the best option for you.

Intermediate to Extensive Metabolizer / Intermediate to Ultra Rapid Metabolizer / Extensive Metabolizer / Extensive to Ultra Rapid Metabolizer / Ultra Rapid Metabolizer

Your body processes (metabolizes) tamoxifen to the active form. A standard dose will generally be suggested.

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 health care providers.

How could the CYP2D6 test result affect my treatment with tamoxifen?

Your health care provider may suggest you take a different medication.

Who is affected? Do different populations respond differently?

Genetic variation in CYP2D6 is dependent on ethnic background. People from Saudi Arabia and Ethiopia are more likely to process tamoxifen quickly; whereas Caucasians are more often found to process tamoxifen slowly.

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What is tamoxifen?

Tamoxifen is a medicine that blocks the effects of the estrogen hormone in the body. It is used to treat breast cancer in women or men. It is also used to reduce the risk of developing breast cancer in those who are at high risk.

Which gene affects my response to tamoxifen?

Variants in the CYP2D6 gene influence the way your body processes (metabolizes) tamoxifen and can affect your response to this medication.

What problems can patients with the CYP2D6 variants have when taking tamoxifen?

Patients who have a CYP2D6 variant that metabolizes tamoxifen quickly may experience more side effects. This can include significant hot flashes, a side effect that is already common for patients taking this drug.

Patients who have a CYP2D6 variant that metabolizes tamoxifen slowly, the medication will not work properly for breast cancer treatment. Patients who have a CYP2D6 variant that metabolizes tamoxifen at an intermediate rate, may be sensitive to drug interactions.

Ask your health care provider for more information about other medications you are taking.

Where can I find more information about tamoxifen?

More information about tamoxifen you might find helpful includes:

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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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