Mechanism of Action of Tamoxifen Drug competes with estrogen in the body for estrogen receptor in breast tissue. Thus the transcription of estrogen responsive genes and growth of cancer cells associated with it inhibited. Stimulation of Ovulation:Tamoxifen blocks the oestrogen receptors in the hypothalamus, it prevents the inhibitory action of oestrogen on release of FSH and LH and therefore the level of FSH and LH increase, which increases the chances of egg development and ovulation. Indications for Tamoxifen 1. Breast cancer (advanced stage in men and in postmenopausal women) 2. Mastalgia 3. Stimulate ovulation 4. Gynecomastia 5. Retroperitoneal fibroid