Goserelin is a prescription drug, not a research chemical. It is sold as Zoladex, an implant that releases the peptide slowly under the skin, and it has been on the market in the United States since 1989. Originally coded ICI 118630 by Imperial Chemical Industries (now AstraZeneca), it remains a standard hormone therapy in oncology and gynecology.
What it is
Goserelin is a synthetic decapeptide — a ten-amino-acid chain — modeled on the body's own gonadotropin-releasing hormone (GnRH, also called LHRH). Two substitutions on the natural GnRH sequence slow its breakdown, so it lasts far longer than the native hormone. It is a GnRH agonist, supplied as the acetate salt.
In the catalog of aliases you'll see ICI 118630, Decapeptide I, and the CAS number 65807-02-5. These all point to the same molecule.
How it works
The mechanism is counterintuitive. GnRH agonists first stimulate the pituitary, then shut it down.
- On first dosing, goserelin activates pituitary GnRH receptors, briefly raising luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and with them testosterone or estrogen. In men this early bump is the so-called testosterone flare.
- With continuous exposure, the receptors down-regulate. LH and FSH fall, and sex hormone levels drop sharply. Per the FDA label, serum testosterone reaches castrate range roughly two to four weeks after the first implant.
The steady, non-pulsatile signal is what flips the system from "go" to "off." That suppression of testosterone (in men) and estradiol (in women) is the therapeutic effect.
What the research and approvals show
This is a well-studied, decades-old medicine, not an experimental peptide. Early clinical work on the LHRH analogue ICI 118630 in advanced prostate cancer was published in the 1980s (PubMed 6135909), and goserelin went on to broad regulatory approval.
FDA-approved uses include:
- Advanced prostate cancer, as palliative hormone therapy (first approved December 1989), and in combination with an anti-androgen for locally confined disease.
- Breast cancer, including premenopausal breast cancer (a 2014 indication) and advanced disease.
- Endometriosis and endometrial thinning ahead of certain gynecological procedures.
It is given subcutaneously as a depot implant in two strengths — 3.6 mg every 4 weeks or 10.8 mg every 12 weeks — so a single placement covers weeks of dosing. Goserelin is also approved or used outside the US (it is an AstraZeneca product marketed widely as Zoladex).
WADA status
Goserelin is banned in sport. The 2026 WADA Prohibited List places GnRH agonists under category S2 (peptide hormones, growth factors, related substances, and mimetics). For male athletes specifically, agents that affect the hypothalamic-pituitary-gonadal axis are prohibited; goserelin falls in that bucket. Prohibited both in and out of competition.
The buyer / quality angle
Goserelin sits in a different category from the gray-market "research" peptides this site usually covers. It is a finished, regulated implant dispensed by pharmacies, with manufacturing held to pharmaceutical standards. There is no legitimate consumer market for loose goserelin powder, and using it without medical supervision would mean self-administering a drug that drives testosterone or estrogen to castrate levels — a profound endocrine change.
If you encounter goserelin sold as a raw peptide or research compound, treat it with skepticism: the identity, purity, and sterility claims of such products are exactly what independent third-party COA testing exists to check, and a sterile implant is not something a powder vendor can credibly supply.
Nothing here is medical or dosing advice. Goserelin is a prescription medicine; decisions about it belong with a qualified clinician.
Sources: [DrugBank](https://go.drugbank.com/drugs/DB00014), [NIH LiverTox](https://www.ncbi.nlm.nih.gov/books/NBK548740/), [FDA Zoladex label](https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/020578s034,020578s035lbl.pdf), [WADA Prohibited List](https://www.wada-ama.org/en/prohibited-list), [PubMed 6135909](https://pubmed.ncbi.nlm.nih.gov/6135909/).