antiestrogenic

Antiestrogenic refers to any substance or action that blocks or opposes the effects of the hormone estrogen. In pharmacology it describes agents that reduce estrogen receptor signaling or estrogen production, thereby diminishing estrogen-driven biological responses. Antiestrogenic effects can be tissue-selective, with different agents acting as antagonists, agonists, or degraders in different tissues.

Mechanisms include direct estrogen receptor antagonism, receptor degradation, or inhibition of estrogen synthesis. Examples of antiestrogenic drugs include selective estrogen receptor modulators such as tamoxifen and raloxifene; SERDs such as fulvestrant that cause receptor degradation; and aromatase inhibitors such as anastrozole, letrozole, and exemestane that lower estrogen production. The net effect is reduced estrogen signaling in target tissues, most notably in breast cancer.

Clinical use centers on estrogen receptor-positive breast cancer, both in treatment and adjuvant settings, and in some cases prevention for high-risk individuals. Raloxifene is used to protect bone and reduce breast cancer risk; tamoxifen has broader breast cancer indications but carries endometrial cancer and thromboembolism risks; aromatase inhibitors can cause bone loss and musculoskeletal symptoms. Therapeutic choice depends on menopausal status, tissue targets, and risk-benefit considerations.