Tamoxifen is a hormone therapy used to treat hormone receptor-positive breast cancer. It can greatly reduce the risk of cancer recurrence (return) and invasive cancer. Some people take tamoxifen to lower the risk of developing breast cancer. The daily oral medication stops cancer cells from using estrogen and progesterone to grow and spread.
Tamoxifen (Nolvadex® or Soltamox®) is a drug that treats hormone receptor-positive (hormone-positive) breast cancer. (Hormone-positive breast cancer is a type of cancer that needs estrogen and/or progesterone to grow.) Healthcare providers also use tamoxifen to help prevent breast cancer in people over 35 who have a high risk of the disease. Since the U.S. Food and Drug Administration (FDA) approved tamoxifen in 1998, it has become one of the most widely used breast cancer treatments.
Tamoxifen can help people with hormone receptor-positive breast cancer. The drug can lower the risk of breast cancer in:
Your healthcare provider will talk with you about your medical history to determine if tamoxifen is right for you.
Millions of people have used tamoxifen to prevent or treat breast cancer. The drug may lower the risk of:
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You must take tamoxifen daily by mouth, preferably at the same time each day. The drug comes in two forms:
Most people take tamoxifen or other hormone therapy for at least five years and sometimes, up to 10 years. Treatment length depends on the specifics of your cancer diagnosis.
Your healthcare provider may recommend taking tamoxifen for five years and then switching to different hormone therapy for several more years.
In addition to lowering the risk of breast cancer and cancer recurrence, tamoxifen:
Tamoxifen side effects may include:
Rarely, tamoxifen may cause serious issues such as:
Research indicates that you’re up to 61% more likely to experience breast cancer recurrence if you don’t take tamoxifen at all or take it incorrectly.
You should call your healthcare provider if you’re taking tamoxifen and experience:
Often, the benefits of taking tamoxifen outweigh the risks. But it depends on your specific situation. While the drug can successfully prevent breast cancer for many, it can also increase the risk of stroke, uterine cancer or blood clotting issues in others.
One research study tested the risks vs. benefits of tamoxifen in a group of 788 women (people assigned female at birth). All of the participants were on tamoxifen and none of them had a history of breast cancer. The study found that the benefits of tamoxifen outweighed the risks for 74% of their participants, but not for 20% of their participants.
During a consultation, a healthcare provider will discuss your medical history in detail. To determine if this type of therapy is right for you, your provider will take the following into consideration:
Tamoxifen may cause birth defects. You shouldn’t take the medication if you’re pregnant or planning to become pregnant. To prevent pregnancy, talk to your healthcare provider about nonhormonal birth control options. (Hormonal contraceptives can fuel the growth of hormone-positive breast cancer.) You’ll need to use contraception while taking tamoxifen and for two months after you stop the medication.
No, tamoxifen is a type of hormonal therapy. It belongs to a class of drugs called selective estrogen receptor modulators (SERMs).
Sometimes, healthcare providers refer to tamoxifen as “chemoprevention.” But usually, chemoprevention drugs aren’t the same as chemotherapy drugs.
While it depends on the person, many individuals report side effects as soon as the first dose.
Certain foods and beverages can make tamoxifen less effective, including:
If you’re taking tamoxifen, you should avoid the foods and beverages listed above.
Tamoxifen stays active for up to two weeks after your last dose. However, it can take about three months to flush out of your system completely.
A note from Cleveland Clinic
Tamoxifen is a highly effective breast cancer treatment. It may significantly lower your risk of breast cancer recurrence or invasive breast cancer. People who are at high risk for breast cancer may take tamoxifen to reduce their chances of getting the disease. Your healthcare provider can discuss whether tamoxifen or another form of hormone therapy is right for you.
Last reviewed by a Cleveland Clinic medical professional on 01/20/2023.
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