Many women have breast
cancer that tests positive for
estrogen receptors (ER+). This means that
estrogen promotes the growth of the breast cancer
cells. Tamoxifen blocks the effects of estrogen on these cells. It is often
called an "anti-estrogen."
Tamoxifen slows or stops the growth of
cancer cells that are already present in the body. It helps keep the original
breast cancer from coming back and helps prevent new cancer in the opposite
breast. It also reduces the risk of breast cancer in women who have a high risk
for this disease.
Why It Is Used
Tamoxifen is used to prevent and treat
breast cancers that test positive for estrogen receptors (ER+). It blocks the
effects that the hormone estrogen has on cancer cells and lowers the chance
that breast cancer will grow. Tamoxifen:
Has been used for decades to treat patients
with advanced breast cancer.
Is used to prevent breast cancer in women who are high-risk
for ER+ breast cancer.
Can be used by women of all ages, both
before and after
Is being studied for the
treatment of other types of cancer.
In rare cases, tamoxifen is used to treat breast pain
(mastalgia), because it reduces estrogen levels that cause breast
swelling. This is an
How Well It Works
Tamoxifen is highly
effective in lowering the risk of breast cancer recurrence. In women who have
already had breast cancer, tamoxifen also lowers the risk of breast cancer in the
opposite breast (contralateral).
postmenopausal women, a two-stage treatment using tamoxifen and then an
aromatase inhibitor, such as anastrozole (Arimidex), exemestane (Aromasin), or
letrozole (Femara) may work better than only taking tamoxifen.
The most common side effects caused by tamoxifen are hot flashes; vaginal dryness, discharge, or irritation; and reduced interest in sex. These side effects are not usually serious, but they can be bothersome.
Other side effects are rare but are more dangerous. These include:
increased risk of
cataract formation and the need for surgery for
See Drug Reference for a full list of side effects. (Drug
Reference is not available in all systems.)
What To Think About
Because tamoxifen can cause changes
in the lining of the uterus, women who use it should have yearly pelvic exams
and should be evaluated further if they experience any abnormal uterine
Tamoxifen may not
work as well if a woman is also taking some types of medicine to treat hot
flashes or depression. If you take tamoxifen, talk with your doctor about any
other medicines you are taking.
Tamoxifen should not
be used if you are pregnant or breast-feeding. Talk with your doctor about birth control if you are taking tamoxifen and could become pregnant.
How this information was developed to help you make better health decisions.