Overview
Tamoxifen is a prescription drug first approved by the Food and Drug Administration (FDA) in 1977 to treat breast cancer. Tamoxifen was later also approved to prevent breast cancer. Tamoxifen is commonly given after surgery (when it is known as an adjuvant treatment) or after chemotherapy to prevent the return of breast cancer. It is also prescribed to some women who are at high risk for breast cancer in order to prevent cancer from developing. It can be taken by women of any age, whether or not they have gone through menopause.

Tamoxifen is not suitable for pregnant or breastfeeding women. The effectiveness of Tamoxifen may be reduced if you are also taking certain medicines that treat hot flashes or depression. Tamoxifen should be used with caution by women who have a history of blood clots or heart attacks.... read more

About two-thirds of breast cancers are estrogen receptor-positive, meaning that they require estrogen in order to grow. Tamoxifen is a member of a class of drugs called selective estrogen receptor modulators, or SERM, that provide hormone therapy for receptor-positive breast cancer. Tamoxifen is believed to work by reducing the effect of estrogen in estrogen receptor positive breast cancers.

How do I take it?
Tamoxifen is taken orally once a day, sometimes for five years or longer. It is best to take it at the same time each day. Tamoxifen is available as a pill or as a liquid.

It is important to use effective birth control while taking Tamoxifen.

Always follow your doctor’s instructions exactly when taking Tamoxifen.

Results
In a summary of 20 different clinical trials involving more than 21,000 women, Tamoxifen was shown to improve overall survival rates by nine percent at the end of 15 years in women with estrogen receptor-positive breast cancer. The summary was updated in 2014.

Tamoxifen reduces the chances of breast cancer returning by 40 to 50 percent in postmenopausal women, and by 30 to 50 percent in premenopausal women. In women who have breast cancer in one breast, Tamoxifen reduces the chance of developing breast cancer in the other breast by 50 percent.

Side effects
Common side effects of Tamoxifen include fatigue, hot flashes, night sweats, mood swings, reduced interest in sex, headaches, fatigue, constipation, and vaginal discharge and dryness. It is worth noting that a 2008 study found that women who experienced night sweats and hot flashes while taking Tamoxifen were 16 percent less likely to experience a recurrence of breast cancer over nine years than women who did not experience these side effects. In this way, some side effects can be seen as a sign that the treatment is working.

Rarely, Tamoxifen can cause very serious side effects including blood clots, stroke and endometrial cancer (uterine) cancer. While you are taking Tamoxifen, notify your doctor immediately if you experience irregular vaginal bleeding, changes in your menstrual cycle, unusual vaginal discharge, or sensations of pain or pressure in your pelvic region, pain or swelling in your legs, shortness of breath, coughing up blood, or sudden dizziness or confusion, difficulty walking or speaking, difficulty seeing in one or both eyes, or sudden tingling, weakness or numbness in your face, arm or leg, especially if the latter only occurs on one side of your body. Note that the risk of developing endometrial cancer increases when women take it for more than five years.

Tamoxifen can also increase the chances that you will develop cataracts in your eyes.

Many drugs can cause allergic reactions which, in the most serious cases, can result in death. Seek immediate medical help if you experience signs of a severe allergic reaction such as difficulty breathing or swelling in the face, throat, eyes, lips or tongue.

Tamoxifen can have two beneficial side effects. It can improve bone density, which reduces the risk of osteoporosis. It can also lower your blood cholesterol, decreasing your chances of developing heart disease.

Tamoxifen Questions

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