What it is
Goserelin is a ten-amino-acid peptide drug built from GnRH, the brain hormone that tells the pituitary to release LH and FSH — recorded in this library as gonadorelin. The Zoladex label gives the two changes that turn a hormone lasting minutes into a drug:
- at position 6, glycine is replaced by a mirror-image (D) serine carrying a bulky tert-butyl group, which resists the enzymes that cut GnRH;
- at position 10, the final glycine becomes aza-glycine amide, a nitrogen-for-carbon swap that protects the end of the chain.
It weighs 1,269 as the free base.
The implant
Goserelin's distinguishing feature is its form. Zoladex is not a liquid. The label describes a 1-mm cylinder of goserelin dispersed in a lactic–glycolic acid copolymer, which it states is completely biodegradable, — preloaded in a single-use syringe with a 16-gauge needle and placed under the skin by a healthcare provider.
| Implant (label) | Goserelin | Release |
|---|---|---|
| Zoladex 3.6 mg | 3.6 mg (3.8 mg acetate), total implant 18 mg | 28 days |
| Zoladex 10.8 mg | 10.8 mg (11.3 mg acetate) | 12 weeks |
The label notes the 3.6 mg implant releases slowly for the first 8 days, then faster and continuously for the rest of the 28.
How it works
GnRH normally reaches the pituitary in pulses. A constant supply has the opposite effect. Per the label, goserelin first raises LH, FSH and testosterone, and then — as the pituitary stops responding — suppresses them:
- in men, testosterone falls into the range seen after surgical castration about 2–4 weeks after starting, and stays there on continued treatment (follow-up beyond 2 years);
- in women, oestradiol falls to postmenopausal levels within about 3 weeks; isolated rises were seen in 10% of trial patients.
That first rise is why the label warns of tumour flare. The receptor blocker ganirelix works the other way, with no initial surge.
What the trials showed
| Use | Evidence on the label |
|---|---|
| Prostate cancer, stage B2–C (with flutamide and radiation) | 466 men: local failure 16% vs 33% at 4 years (P < 0.001); median disease-free survival 4.4 vs 2.6 years |
| Advanced prostate cancer | Controlled studies against surgical castration: similar hormonal and objective responses and similar survival |
| Advanced breast cancer, premenopausal | SWOG-8692, interim analysis of 124 women vs ovary removal: response 22% vs 12%; median survival 33.2 vs 33.6 months |
| Endometriosis | Two trials against danazol: ≥50% lesion reduction 63% vs 42% and 62% vs 51%; symptoms reduced by about 84% by the end of treatment |
| Endometrial thinning | Trial 0022, 358 premenopausal women before ablation |
Safety
The label's warnings: tumour flare in the first weeks (including ureteral obstruction and spinal cord compression); raised blood sugar and diabetes and heart attack, sudden cardiac death and stroke reported with GnRH analogues in men; high calcium in patients with bone metastases; severe skin reactions including Stevens–Johnson syndrome; possible QT prolongation; injection-site and vascular injury; depression; and pregnancy must be excluded before use for non-cancer conditions. The most common reactions in men were hot flashes, sexual dysfunction, decreased erections and urinary symptoms.
Where it stands
Drugs@FDA lists two goserelin applications on 2026-10-02, both Zoladex and both held by TerSera: 3.6 mg (NDA 019726, 1989-12-29) and 10.8 mg (NDA 020578, 1996-01-11). No generic is listed. PubMed returns 2,162 records for goserelin, 437 tagged as randomised controlled trials — one of the larger trial records among this library's approved drugs.
Related reading
Goserelin sits with the other GnRH agonists in this library, leuprolide and triptorelin, and the antagonist ganirelix. The hormone they all copy is gonadorelin; the signal upstream of it is kisspeptin.