Goserelin is a synthetic GnRH agonist decapeptide analog (MW ~1269.4 g/mol) delivered as a biodegradable PLGA implant (Zoladex) injected subcutaneously in the anterior abdominal wall. It is FDA-approved for advanced prostate cancer, breast cancer, endometriosis, and endometrial thinning before ablation. Like other GnRH agonists, goserelin operates through a "flare then suppression" mechanism, achieving castrate levels of sex steroids with continued administration. The implant formulation is available in 1-month (3.6 mg) and 3-month (10.8 mg) presentations.
Category: Reproductive / Hormonal. Evidence rating: A (strong human clinical data).
Clinical status: FDA-approved (Zoladex for prostate cancer, breast cancer, endometriosis, endometrial thinning)
Goserelin is a GnRH agonist with a D-Ser(tBu) substitution at position 6 and an azaglycine amide at position 10, providing enhanced potency and enzymatic resistance compared to native GnRH. The mechanism follows the "flare then suppression" paradigm: initial administration causes transient…
Safety considerations: Hot flashes (up to 57-75% of patients); Decreased bone mineral density with prolonged use; Initial disease flare (1-2 weeks): tumor flare in prostate cancer with potential spinal cord compression, bone pain exacerbation.
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-08-12.
Related peptides: Kisspeptin, Gonadorelin, Oxytocin.
Compare: Goserelin vs Kisspeptin, Goserelin vs Gonadorelin, Goserelin vs Oxytocin.
The Zoladex implant is a small biodegradable cylinder injected subcutaneously into the anterior abdominal wall using a pre-loaded syringe with a 16-gauge needle. The procedure takes seconds and is performed in a clinic. The implant dissolves over 28 days (3.6 mg) or 12 weeks (10.8 mg), continuously releasing goserelin.
In the first 1-2 weeks of goserelin treatment, LH and testosterone levels temporarily rise (the "flare"), which can worsen prostate cancer symptoms including bone pain and urinary obstruction. This is typically prevented by starting an anti-androgen (e.g., bicalutamide or flutamide) 1-2 weeks before the first goserelin injection and continuing for 2-4 weeks.
Goserelin is used off-label in IVF protocols for pituitary downregulation before controlled ovarian hyperstimulation. There is also evidence from the POEMS/SWOG S0230 trial (Moore et al., NEJM 2015, PMID: 25738669) that goserelin during chemotherapy may protect ovarian function and preserve fertility in premenopausal breast cancer patients.