FSH vs Leuprolide

Binds FSH receptors on Sertoli cells in testes to support sperm maturation and inhibin B production. In women, binds granulosa cell FSH receptors to drive follicular growth and estradiol production.

FSH (follicle-stimulating hormone) is an endogenous heterodimeric glycoprotein hormone produced and secreted by pituitary gonadotrophs, composed of a non-covalently associated common alpha subunit shared with LH, TSH, and hCG, and a unique FSH-specific beta subunit that confers receptor specificity; it is the primary regulator of gametogenesis in both sexes, acting on ovarian granulosa cells and testicular Sertoli cells to drive reproductive development. FSH activates its cognate receptor (FSHR) through cAMP-mediated signaling to stimulate follicular maturation and estradiol synthesis in the ovary via aromatase upregulation, and to support spermatogenesis in the testis by promoting Sertoli cell function and germ cell proliferation; FSH levels rise dramatically at menopause as negative feedback from ovarian estrogen declines. A Cochrane systematic review and meta-analysis established that recombinant FSH preparations are clinically equivalent to urinary-derived gonadotropins for ovarian stimulation in assisted reproductive technology cycles, providing the evidence base underlying current ART practice; this review supports the use of recombinant FSH as the standard of care for controlled ovarian hyperstimulation. FDA-approved recombinant FSH preparations — follitropin alfa (Gonal-f) and follitropin beta (Follistim) — require a prescription and are indicated for ovulation induction and ART in women and for hypogonadotropic hypogonadism in men; endogenous FSH is not administered as a therapeutic agent, and research-grade recombinant FSH is used as a cell culture tool and reproductive biology research compound.

Continuous GnRH receptor stimulation causes receptor desensitization and downregulation. This suppresses LH/FSH → testosterone/estrogen to castrate levels. Short-term pulsatile use can transiently stimulate the axis before suppression occurs.

Leuprolide (leuprorelin; Lupron) is a synthetic nonapeptide GnRH agonist (D-Leu6, des-Gly10-GnRH ethylamide) designed as a superagonist of the gonadotropin-releasing hormone receptor; paradoxically, its continuous non-pulsatile receptor occupation produces profound hypogonadotropism by causing receptor downregulation and pituitary desensitization — the opposite effect of endogenous pulsatile GnRH release — resulting in medical castration levels of sex steroids. Continuous LHRH receptor agonism initially produces a testosterone or estrogen flare before pituitary downregulation suppresses LH and FSH secretion, reducing testosterone to castrate levels in men and estrogen to postmenopausal levels in women within 2–4 weeks; this chemical hypogonadism forms the basis for its use across hormone-sensitive conditions including prostate cancer, endometriosis, uterine fibroids, and central precocious puberty. A landmark randomized controlled trial published in the New England Journal of Medicine compared leuprolide against diethylstilbestrol for metastatic prostate cancer and demonstrated equivalent efficacy with a markedly superior cardiovascular side-effect profile, establishing the pivotal evidence base that led to FDA approval and positioned GnRH agonists as the preferred hormonal therapy for prostate cancer. Leuprolide (Lupron, AbbVie; and generic formulations) is FDA-approved and requires a prescription; approved indications include advanced prostate cancer, endometriosis, uterine fibroids, central precocious puberty, and other hormone-sensitive conditions; it is available as daily subcutaneous injection, monthly depot, and multi-month depot formulations.