Tamoxifen: Hormone Therapy Medication for Breast Cancer Treatment

A pink ribbon have a word of "Tamoxifen"

There are more than 3.1 million breast cancer survivors in the United States. This includes women still being treated and those who have completed treatment. Tamoxifen is the most-prescribed selective estrogen receptor modulator (SERM) used in the treatment of breast cancer.   

Tamoxifen is used to treat the following conditions:

  • Cancer of the ovary/ovaries
  • Cancer in the lining of the uterus
  • Metastatic breast carcinoma
  • Intraductal breast cancer
  • Hormone receptor positive breast cancer
  • Prevention of breast cancer in women who are at high risk for developing cancer

Generic tamoxifen  is a synthetic non-steroidal antiestrogen; a hormone therapy medication which prevents estrogen from encouraging the growth of breast cancer cells.  It does this by attaching to the hormone receptors in cancer cells, which then blocks estrogen from attaching to the receptor.  The result is that the tumor growth is stopped or slowed down because it cannot get access to the hormone (estrogen) it needs in order to grow.

According to the American Cancer Society, the estimates for breast cancer in the United States for 2019 are: 

  • About 268,600 new cases of invasive breast cancer will be diagnosed in women. 
  • About 62,930 new cases of carcinoma in situ (CIS) will be diagnosed (CIS is non-invasive and is the earliest form of breast cancer). 

How to take tamoxifen

It is important to follow your doctor’s guidelines when taking tamoxifen.

Taken once or twice a day, this medication is usually taken for a five year period unless specified otherwise by your doctor.    The dose is based upon your response to treatment and your medical diagnosis.

See pricing and information:

Tamoxifen – 10 mg tablets 

Tamoxifen – 20 mg tablets

Always take tamoxifen at the same time every day.   Those with breast cancer which has spread to other parts of the body may notice an increase in pain or disease flare-ups when therapy is first begun with tamoxifen.   Any symptoms such as increased tumor size, new tumors, or increased bone pain should be reported to your doctor quickly.

Tamoxifen side effects

While some people who take this medication may experience mild to no serious side effects, here are some of the known side effects which may occur:

  • Leg cramps or muscle pain in other parts of your body
  • Headache
  • Nausea
  • Hot flashes
  • Loss of sexual ability or interest

You should tell your doctor immediately if you experience any of the following side effects:

  • Change in vision oreye pain
  • Swelling of feet or ankles
  • Signs of liver disease (yellowing eyes and skin, stomach pain, non-stop vomiting or nausea)
  • Mood change
  • Extreme fatigue

This is not a complete list of side effects, so speak to your doctor and pharmacist about what other side affects you may experience.

Some test results for other conditions, such as thyroid tests, may be affected by tamoxifen, so always tell the people doing your blood work at the laboratory that you are taking tamoxifen.

Certain medications may interfere with tamoxifen, such as SSRI antidepressants, medications used to prevent seizures, blood thinners, hormonal forms of birth control, and others.  Speak to your pharmacist and let them know what medications and supplements you are taking.

Visit the American Cancer Society at for more information about breast cancer.

This article contains medical information provided to help you better understand this particular medical condition or process, and may contain information about medication often used as part of a treatment plan prescribed by a doctor.  It is not intended to be used as either a diagnoses or recommendation for treatment of your particular medical situation.  If you are unwell, concerned about your physical or mental state, or are experiencing symptoms you should speak with your doctor or primary health care provider. If you are in medical distress please contact emergency services (such as 911).

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