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Tamoxifen is available in 10 mg and 20 mg tablets. When
used for early-stage breast cancer, tamoxifen is usually prescribed at 20 mg a
day for 5 years. Tablets may be taken once or twice a day.
Tamoxifen is the most commonly used
hormone therapy for the treatment of
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.
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:
In rare cases, tamoxifen is used to treat breast pain
(mastalgia), because it reduces estrogen levels that cause breast
swelling. This is an
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 decreased 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:
See Drug Reference for a full list of side effects. (Drug
Reference is not available in all systems.)
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. Discuss birth control with your
doctor if you are taking tamoxifen and could become pregnant.
Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.
June 28, 2011
Sarah Marshall, MD - Family Medicine & Douglas A. Stewart, MD - Medical Oncology
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