Taking tamoxifen for five years does not necessarily stop your periods. Tamoxifen is a drug that inhibits tumor growth by preventing the body’s normal estrogen and progesterone from binding to hormone receptors on the surface of breast cancer cells, making it impossible for estrogen to stimulate cancer cells. Tamoxifen does not inhibit estrogen production, so taking Tamoxifen for five years will not necessarily stop your period. Tamoxifen has a competitive relationship with estrogen and will bind to estrogen receptors on the surface of cancer cells, thus making the estrogen level in the blood high, and some patients may have abnormal uterine bleeding while taking tamoxifen. However, due to age and individual differences in the use of the drug, some people may experience menstrual disorders or stop menstruation after taking the drug. Thickening of the uterine lining may occur during tamoxifen use, leading to menstrual disorders, but there is no need to worry too much. It is recommended that the gynecological ultrasound be checked regularly during the medication period, and the medication should be used under the guidance of the doctor.