Tamoxifen

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Chemical name: Tamoxifen

Pill brand names: Nolvadex, Apo-Tamox, Tamofen, Tamone

Liquid brand name: Soltamox

Class: SERM (selective estrogen receptor modulator) hormonal therapy. Evista and Fareston are other SERMs.

How it works: SERMs block the effects of estrogen in the breast tissue by attaching to the estrogen receptors in breast cells.

Uses: Tamoxifen, used to treat men and both premenopausal and postmenopausal women, typically is used to:

  • reduce the risk of early-stage, hormone-receptor-positive breast cancer coming back after surgery and other treatments
  • shrink large, hormone-receptor-positive breast cancers before surgery
  • treat advanced-stage, hormone-receptor-positive breast cancer, including metastatic breast cancer
  • reduce breast cancer risk in undiagnosed women at higher-than-average risk of developing breast cancer

Tamoxifen usually is taken for 5 to 10 years, depending on a woman’s menopausal status. The American Society of Clinical Oncology recommends that:

  • newly diagnosed premenopausal and perimenopausal women take 5 years of tamoxifen as their first hormonal therapy; after this first 5 years is done, the hormonal therapy taken for the second 5 years (for a total of 10 years of hormonal therapy) would be determined by the woman’s menopausal status:
    • postmenopausal women could take another 5 years of tamoxifen or switch to an aromatase inhibitor for 5 years
    • pre- and perimenopausal women would take another 5 years of tamoxifen
  • newly diagnosed postmenopausal women have several options:
    • take tamoxifen for 10 years
    • take an aromatase inhibitor for 5 years; right now there isn’t enough evidence to recommend taking an aromatase inhibitor for 10 years
    • take tamoxifen for 5 years, then switch to an aromatase inhibitor for another 5 years (for a total of 10 years of hormonal therapy)
    • take tamoxifen for 2 to 3 years, then switch to an aromatase inhibitor for another 5 years (for a total of 7 to 8 years of hormonal therapy)
  • postmenopausal women who started taking an aromatase inhibitor but didn’t finish 5 years of treatment can switch to tamoxifen to complete 5 years of hormonal therapy
  • postmenopausal women who started taking tamoxifen but didn’t finish 5 years of treatment can switch to an aromatase inhibitor and take it for 5 years (for a total of 7 to 8 years of hormonal therapy)

How it's given: Tamoxifen is taken orally as a pill or as a liquid.

Additional information: About 10% of people have an abnormal CYP2D6 gene that makes a version of the CYP2D6 enzyme that doesn’t function as well as it should. Having a low-functioning CYP2D6 enzyme might keep a person from getting the full benefit of tamoxifen. In 2018, the Clinical Pharmacogenetics Implementation Consortium, an international group of scientists that issues guidelines on the effects of genetic factors on reactions to drugs, issued a guideline on using CYP2D6 genotype information to make decisions about prescribing tamoxifen after surgery to treat hormone-receptor-positive breast cancer. The guideline strongly recommends that people with an abnormal CYP2D6 genotype that makes them less able to metabolize tamoxifen be treated with a different type of hormonal therapy, such as an aromatase inhibitor. You may want to ask your doctor about being tested for this genetic abnormality if you are considering taking tamoxifen.

Also, certain medications can block the activity of the CYP2D6 enzyme, including antidepressants known as SSRIs and SNRIs, as well as Benadryl (chemical name: diphenhydramine) and Tagamet (chemical name: cimetidine). Make sure you tell your doctor about ALL other medicines you're taking if you're considering taking tamoxifen to make sure you get the full benefit of treatment.

Side effects:

Read more about tamoxifen.

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