Leuprolide

Native GnRH is released in pulses (every 90-120 minutes) from the hypothalamus, and pulsatile GnRH stimulation is required for normal gonadotropin secretion. Continuous GnRH receptor stimulation by leuprolide depot causes receptor internalization and downregulation (desensitization). Within 2-4 weeks, pituitary GnRH receptors are profoundly desensitized, LH and FSH secretion falls to castrate levels, and gonadal steroid production ceases. Initial treatment produces a testosterone or estrogen "flare" (1-2 weeks) before suppression occurs.

In males, leuprolide-induced LH suppression reduces testicular testosterone production to castrate levels (<50 ng/dL). In females, FSH and LH suppression creates a hypoestrogenic state comparable to surgical menopause. These hormonal manipulations deprive hormone-sensitive tumors (prostate cancer, ER+ breast cancer) of growth stimuli, and arrest GnRH-dependent conditions (endometriosis, uterine fibroids, precocious puberty). Suppression is fully reversible within weeks to months of stopping treatment.

Leuprolide depot formulations use microsphere or in-situ polymer matrix technology to provide controlled, sustained peptide release over 1, 3, 4, or 6 months. The depot injection creates a subcutaneous or intramuscular reservoir that slowly hydrolyzes, releasing leuprolide over the dosing interval. This achieves consistent plasma concentrations maintaining GnRH receptor desensitization without the inconvenience of daily injections.

Androgen deprivation therapy (ADT) with leuprolide or other GnRH agonists/antagonists is the backbone of treatment for metastatic prostate cancer, hormone-sensitive prostate cancer, and high-risk localized disease. Combined with antiandrogens and newer agents (enzalutamide, abiraterone), leuprolide-based ADT extends survival significantly. Testosterone monitoring (<50 ng/dL target) confirms adequate suppression.

Six-month courses of leuprolide depot reduce endometriotic lesion size and pain symptoms in 80-90% of patients by creating a hypoestrogenic environment. Fibroids shrink 30-65% in volume after 3-6 months, facilitating surgical management. Add-back therapy (low-dose estrogen + progestogen) prevents bone loss with long-term use while maintaining therapeutic efficacy. Leuprolide is also first-line for central precocious puberty to prevent premature bone fusion and early sexual development.

Leuprolide has been studied for thymic regeneration in aging, sex steroids suppress thymic function, and leuprolide-mediated castration restores thymopoiesis and naive T-cell output in animal models and HIV patients. This "immunological rejuvenation" through temporary androgen suppression is being studied as a strategy to restore immune function in immunocompromised or elderly patients.