Tamoxifen is a hormone therapy drug that can be used to treat hormone receptor-positive breast cancers in women and men. It works by blocking estrogen from attaching to the receptors of cancer cells, which slows or stops tumor growth.

Tamoxifen is a pill that is taken daily, usually for 5-10 years, but the benefits last long after treatment ends.

A recent study showed that taking tamoxifen for 10 years reduced the risk of breast cancer recurrence and death more than taking tamoxifen 5 years. These findings led to increased use of tamoxifen for more than 5 years, especially among premenopausal women who can’t take aromatase inhibitors and those with higher stage breast cancers.

However, taking tamoxifen for a longer time also means a continued risk of health effects, such as endometrial cancer, and for premenopausal women, it may also impact fertility. So, discuss the benefits and risks of taking tamoxifen for more than 5 years with your health care provider.

And before you begin taking tamoxifen, it’s important to talk with your health care team about possible side effects and how to manage them.

Common side effects of tamoxifen in women include hot flashes, night sweats, vaginal dryness or discharge and a lower sex drive. Men may also experience hot flashes and a decreased sex drive, as well as headaches, nausea and vomiting.

Rare, but potentially serious side effects include blood clots in the lungs, called a pulmonary embolism, or in the major veins of the legs, called deep vein thrombosis, cataracts and stroke. Other rare side effects for women include bone loss in premenopausal women and uterine cancer. Although rare, because some women may develop uterine cancer from taking tamoxifen, routine gynecological exams are recommended. Another rare side effect for men is a skin rash.

It may help to keep in mind that there are many benefits to taking tamoxifen, including a lower risk of recurrence, so be sure to let your health care team know if you experience any side effects as many can be treated or managed with lifestyle changes.

For more information, visit the Tamoxifen page within the Treatment section of komen.org.