Leuprolide

Leuprolide is a superagonist at the pituitary GnRH receptor. When you first give it, it strongly stimulates the receptor and causes a transient surge in LH, FSH, and sex hormones, the so-called flare. With continuous exposure, the pituitary internalizes and downregulates its GnRH receptors and becomes desensitized, so within roughly two to four weeks LH and FSH plummet and gonadal testosterone or estrogen falls to near-castrate levels. In prostate cancer, removing testosterone starves androgen-dependent tumor cells; in endometriosis and fibroids, dropping estrogen shrinks hormone-driven tissue and eases pain.