According to the National Cancer Institute (NCI), tamoxifen, an oral medication approved by the U.S. Food and Drug Administration, has been used for more than 30 years to treat breast cancer in both women and men. This drug is known as a selective estrogen receptor modulator (SERM); specifically, it blocks the female hormone estrogen from acting on breast cells in breast cancers that are hormone receptive or hormone positive. This medication is used also in women who have a particularly high risk of developing breast cancer as well as extensive breast tissue growth in men (gynecomastia).
Uterine Cancer
Tamoxifen stimulates estrogen in the lining of the uterus. According to the NCI, women who take tamoxifen are at an increased risk for two types of uterine malignancy: endometrial (uterine lining) cancer and uterine sarcoma (uterine wall). The risk is considered small compared with the drug's benefits, which are viewed usually as outweighing the potential consequences.
Circulatory Disorders
The NCI's breast cancer prevention trial found that being on tamoxifen for several years slightly increases the risk for blood clots (venous thrombosis and pulmonary emboli) and strokes. Changes in terms of easy bruising or bleeding easily also may result. This effect is prominent when tamoxifen is combined with chemotherapy. Thus, it is a contraindication to prescribe tamoxifen to individuals who have a history of blood clots or circulatory conditions of this type.
Hot Flashes
Some of the most common reported side effects of tamoxifen are menopausal symptoms such as hot flashes, irregular or absent menstrual periods, vaginal discharge, vaginal dryness and changes in mood. These symptoms will vary according to the individual, but they are not considered to be severe.
Gastric Distress
At times, stomach problems such as nausea and vomiting, an upset stomach or indigestion may be reported, but these symptoms usually are not severe. Abdominal pain or discomfort also may be experienced sporadically.
