Goserelin (Zoladex)

Prescription

Goserelin acetate (brand name Zoladex) is a synthetic decapeptide analog of gonadotropin-releasing hormone (GnRH/LHRH). Like other GnRH agonists, it carries substitutions at positions 6 and 10 (D-serine(tBu) at position 6 and an azaglycine amide at the C-terminus) that make it far more potent and resistant to enzymatic breakdown than the native hormone. It is formulated in a distinctive way: a small biodegradable cylinder of lactide-glycolide copolymer, pre-loaded in a syringe, is injected under the skin of the abdomen, where it slowly dissolves and releases drug over 1 or 3 months. Goserelin's pharmacology follows the same biphasic principle as leuprolide and triptorelin. Native GnRH must be released in pulses to keep the pituitary producing LH and FSH; a continuous, non-pulsatile agonist signal first causes a transient surge (the 'flare') and then downregulates and desensitizes the GnRH receptor, shutting the axis down. The result is a reversible medical suppression of sex hormones — testosterone to castrate levels in men, estradiol to postmenopausal levels in women. Goserelin is FDA-approved across an unusually broad set of indications: advanced prostate cancer, hormone-receptor-positive breast cancer in pre- and perimenopausal women, endometriosis, endometrial thinning before ablation, and (with iron) the management of uterine fibroids before surgery. In premenopausal breast cancer it is a cornerstone of ovarian function suppression, allowing the ovaries to be 'switched off' so that estrogen-driven tumors are starved of their fuel, often alongside tamoxifen or an aromatase inhibitor. Side effects flow predictably from low sex-hormone levels: hot flashes, reduced libido, injection-site reactions, and — with prolonged use — bone mineral density loss. In men, an initial testosterone flare can transiently worsen prostate cancer symptoms, so an anti-androgen is usually given for the first few weeks. All of these effects are managed under specialist oncology or gynecology care, and hormonal recovery generally follows discontinuation.