Goserelin: evidence, FDA status and research

A hormone-lowering implant used for prostate cancer, breast cancer and endometriosis. Controlled trials support these uses.

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Goserelin is a hormone-suppressing implant used in prostate cancer, premenopausal breast cancer and endometriosis, sometimes discussed as a way to protect ovaries during chemotherapy.

Studies say

Randomised trials show goserelin lowers sex hormones to post-menopausal or castrate levels and matches chemotherapy for survival in hormone-sensitive premenopausal breast cancer, which supports the approvals and the A grade.

Why grade A. Goserelin's approvals rest on randomised trials in prostate and breast cancer and endometriosis. The cited ZEBRA trial randomised 1,640 premenopausal women with node-positive early breast cancer to goserelin or CMF chemotherapy and found equivalent disease-free and overall survival in those with hormone-receptor-positive tumours. ¹²

FDA. Goserelin is FDA-approved as Zoladex, a subcutaneous implant first approved in 1989. Its labelled indications are palliative treatment of advanced prostate cancer, use with flutamide and radiotherapy in locally advanced prostate cancer, endometriosis, thinning of the uterine lining before ablation surgery, and palliative treatment of advanced breast cancer in pre- and perimenopausal women. ²

Written from 2 cited sources. Fact-checked 2026-10-27: 12 claims checked, 0 corrected. Last refreshed 2026-10-27. Not physician reviewed.

What this means for you

What people take it for: Prostate and breast cancer, and endometriosis
Can a US doctor prescribe it?: Yes, FDA approved for prostate cancer, endometriosis and other uses.
Properly tested in people?: Yes, in large controlled trials; one covered 1,640 women.

Evidence checklist

Randomised controlled trial ZEBRA, goserelin versus CMFyes
Human study over 100 people ZEBRA randomized 1,640 womenyes
More than one research group Trials across prostate, breast, endometriosisyes
Clinical outcomes, not surrogate markers Disease-free and overall survivalyes
Human safety data beyond case reports Decades of label and trial datayes

Drawn from the cited studies below. A dash means the sources give no information.

What it is

Goserelin is a lab-made copy of GnRH, with ten amino acids. GnRH stands for gonadotropin-releasing hormone. It comes from the hypothalamus. It tells the pituitary to release signals. These drive testosterone and oestrogen production. ICI Pharmaceuticals made it. That firm became Zeneca, then AstraZeneca. The brand name is Zoladex. ²

It is a small rod. A needle places it under the skin of the abdomen. It comes in one-month and three-month versions. It is not a liquid shot. The rod dissolves slowly. It releases the peptide at a steady rate. ²

How it works

Steady exposure to a GnRH agonist does the opposite of natural pulses of the hormone. For the first week or two, the pituitary releases a surge of luteinising hormone (LH). Testosterone or oestrogen rise. This flare can briefly worsen cancer symptoms. After that, the pituitary receptors stop responding (downregulate). LH falls. The testes or ovaries stop making hormones. In men, testosterone reaches castrate levels within about three to four weeks. In women, oestrogen drops to post-menopausal levels. ²

What human research shows

The ZEBRA trial compared two years of goserelin with six cycles of CMF chemotherapy. It enrolled 1,640 women before menopause who had early breast cancer in the lymph nodes (node-positive). Its survival results came out in 2003. Women whose tumours had oestrogen receptors did equally well on either treatment, for both disease-free and overall survival. Women whose tumours lacked those receptors did worse on goserelin. This is expected with a hormone treatment. The drug caused menopausal symptoms. Chemotherapy caused nausea, hair loss and infections. ¹

The prostate cancer approvals rest on two kinds of trials. Some showed that testosterone fell as far as after surgical castration. One tested goserelin plus flutamide with radiotherapy, in locally advanced disease. The approved uses for endometriosis and endometrial thinning rest on randomised trials. They showed symptom relief. They also showed a thinner uterine lining. ²

Study	Model	Finding
ZEBRA survival analysis, 2003	Humans, n=1,640 premenopausal women with node-positive breast cancer, randomised goserelin versus CMF	Equivalent disease-free and overall survival in oestrogen-receptor-positive disease; inferior outcomes with goserelin in receptor-negative disease. ¹
Zoladex prescribing information, 2026	FDA label summarising registration trials	Testosterone suppression to castrate levels in prostate cancer and symptom improvement in endometriosis supported the approved indications. ²

Safety

The common side effects come from hormone suppression. These are hot flushes, loss of libido and mood changes. Men can have erectile dysfunction. Women can have vaginal dryness. With long use, bone mineral loss can occur. The first flare can worsen bone pain or urinary blockage in men with metastatic prostate cancer. So doctors sometimes add an anti-androgen. The label also warns about high blood sugar and QT prolongation. It warns of heart risk in men on androgen deprivation. Doctors must rule out pregnancy first in women. ²

Questions for your clinician

Would goserelin or chemotherapy suit my tumor receptor status?
How will my bone density be followed during treatment?
What happens to bone pain in the first weeks of prostate treatment?

Questions people ask

Is goserelin FDA-approved?

Yes, as Zoladex, since 1989. The current label covers advanced and locally advanced prostate cancer, endometriosis and endometrial thinning before ablation. It also covers advanced breast cancer in pre- and perimenopausal women. ²

How does goserelin compare with chemotherapy in breast cancer?

In the 1,640-woman ZEBRA trial, two years of goserelin gave the same disease-free and overall survival as CMF chemotherapy. This was in women before menopause whose tumours had oestrogen receptors. In tumours without them, chemotherapy was better. ¹

Why do symptoms sometimes get worse at first?

A GnRH agonist first stimulates the pituitary before it shuts it down. So testosterone or oestrogen goes up for a week or two. In men with metastatic prostate cancer, this flare can briefly worsen bone pain or urinary symptoms. ²

How is goserelin given?

It is a small solid implant. A needle places it under the skin of the abdomen. It comes in a one-month or a three-month version. It dissolves and releases the drug steadily. ²

Citations

Kaufmann 2003, European Journal of Cancer: survival analyses from the ZEBRA study, goserelin versus CMF in premenopausal node-positive breast cancer doi.org
FDA 2026: Zoladex (goserelin implant) prescribing information accessdata.fda.gov