About Tamoxifen

What is tamoxifen?

Tamoxifen is a drug that reduces and/or stops the effects of estrogen (a female hormone) in the body. It was developed over 30 years ago and has been used to treat both advanced and early stage breast cancer. More recently, tamoxifen is being used as an adjuvant, or additional, therapy following primary treatment for early stage breast cancer. It is also used to try to prevent breast cancer in women who are at high risk.

Tamoxifen is taken by mouth in tablet form and is usually prescribed as a single daily dose.

How is tamoxifen used for breast cancer treatment?

As a breast cancer therapy, tamoxifen works against the effects of estrogen, which has been shown to promote the growth of breast cancer cells. It is often called an anti-estrogen:

  • As a treatment for breast cancer, the drug slows or stops the growth of cancer cells that need estrogen to grow and spread.

  • As adjuvant therapy, tamoxifen has been shown to help prevent the development and recurrence of breast cancer. Research has shown that when tamoxifen is used as adjuvant therapy for early stage breast cancer, it not only prevents the recurrence of the original cancer but also prevents the development of new cancers in the opposite breast, in many cases.

  • As a preventive therapy, tamoxifen has been shown to help prevent the development of breast cancer in high-risk women.

Additional benefits of tamoxifen

While tamoxifen acts against the effects of estrogen in breast tissue, it acts like estrogen in other body systems. According to the National Cancer Institute, women who take tamoxifen may experience many of the beneficial effects of menopausal estrogen replacement therapy, such as a lowering of blood cholesterol and a slowing of bone loss (osteoporosis).

What are the possible side effects of tamoxifen?

Women considering taking tamoxifen should consult their doctor. Different women experience side effects differently. Some of the more common side effects may include:

  • Hot flashes and sweats

  • Nausea and vomiting

  • Loss of appetite

  • Weight gain

  • Vaginal discharge

  • Irregular menstrual cycles

  • Fatigue (extreme tiredness) 

  • Headache

  • Vaginal dryness

  • Irritation of skin around the vagina

Less common side effects may include:

  • Blood clots

  • Depression

  • Eye problems

  • Uterine or endometrial cancers

  • Other cancers

Some doctors and researchers caution, however, that tamoxifen therapy may not be appropriate for all women who are at increased risk for breast cancer. Consult your doctor for more information regarding your individual case.


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