Tamoxifen does not necessarily lead to amenorrhea after taking it; some patients may experience adverse effects such as amenorrhea, but it is not clear how long it takes for amenorrhea to occur after taking Tamoxifen. Tamoxifen is a non-steroidal anti-estrogen drug, an endocrine therapy drug, belongs to the hormone receptor modulators. This drug binds to estrogen receptors and inhibits breast cancer cell proliferation, thus achieving the purpose of anti-tumor therapy. You may not experience amenorrhea after taking tamoxifen, and normal menstruation will not affect the efficacy of tamoxifen. Since the drug has anti-estrogenic effect, it may cause menstrual disorders, amenorrhea, vaginal dryness, and endometrial hyperplasia, so when taking the drug, regular ultrasound examination is needed to clarify the thickness of the endometrium. If abnormal thickening occurs, a biopsy may be necessary; Some patients may experience adverse reactions such as facial flushing, vulvar itching, menstrual disorders, amenorrhea, leukorrhea, vaginal bleeding, etc. after taking tamoxifen, but there is no fixed time or probability as to how long it will take to become amenorrheic after taking the drug. The drug needs to be used under the guidance of a doctor, and if adverse reactions such as amenorrhea after taking Tamoxifen occur, you should seek medical attention.