antiandrogen

An antiandrogen is a substance that inhibits the action of androgens, male sex hormones, by blocking androgen receptor signaling or by reducing the production or availability of androgens. Antiandrogen therapy is used in conditions driven by androgen activity, including prostate cancer, hirsutism, acne, and certain transgender and intersex conditions.

Mechanisms fall into several categories. Androgen receptor antagonists, also called AR inhibitors, bind to the androgen receptor and prevent testosterone and dihydrotestosterone from activating target genes. Examples include nonsteroidal agents such as flutamide, bicalutamide, nilutamide, enzalutamide, and apalutamide, and the steroidal agent cyproterone acetate. Some regimens decrease gonadotropin output with progestins, lowering testosterone production. 5-alpha-reductase inhibitors like finasteride and dutasteride reduce the conversion of testosterone to dihydrotestosterone, diminishing DHT-driven effects. Androgen synthesis inhibitors, such as abiraterone, inhibit enzymes required for androgen production, further lowering circulating androgens.

Medical uses include treatment of advanced prostate cancer as part of androgen deprivation therapy, sometimes in combination with GnRH agonists or antagonists. They are also used to treat hirsutism, acne, or androgenic alopecia in women, and in some regions as part of gender-affirming therapy to suppress masculinization in transgender women. Spironolactone, a diuretic with antiandrogen effects, is commonly used for dermatologic indications such as hirsutism in some settings.

Common adverse effects vary by mechanism and drug but often include hot flashes, fatigue, reduced libido, erectile dysfunction, and breast tenderness or gynecomastia. Hepatotoxicity has been reported with some agents (notably flutamide). 5-alpha-reductase inhibitors can cause sexual dysfunction and rare mood effects; spironolactone has hyperkalemia risk; and some agents carry thrombotic risk (cyproterone acetate).