Does Zoladex actually work?

For the things it is approved for, yes, and the evidence is unusually solid because its trials had real comparison groups. In men with high-risk prostate cancer, adding three years of goserelin to radiotherapy left 58.1% alive at ten years against 39.8% on radiotherapy alone. In women with endometriosis it shrank lesions in 63% against 42% on the older drug danazol. In premenopausal breast cancer it matched chemotherapy when the tumour was driven by oestrogen — and was clearly worse than chemotherapy when it was not.

What are the side effects of Zoladex?

Hot flushes and sweats are by far the most common, and they beat every comparison group they were tested against: 62% of men on goserelin versus 53% of men who had their testicles removed, and 96% of women with endometriosis versus 67% on danazol. Loss of sex drive, low mood, headache and weight gain are all common. The one that matters most over time is bone loss, at about 1% a month on a six-month course. The rare but serious list includes skin reactions that strip the skin, bleeding where the implant goes in, and too much calcium in the blood in people whose cancer has reached the bones.

Does Zoladex make the cancer worse at first?

Briefly, and this is the strangest thing about the drug. Goserelin is a copy of the natural signal that switches the sex glands on, so the first implant pushes the hormone up before the switch jams shut. In the controlled breast cancer trial, this tumour flare was recorded in 23% of the 57 women on goserelin and 4% of the 55 who had their ovaries removed instead. In men it can mean a few weeks of worse bone pain or urinary trouble and, rarely, pressure on the spinal cord. The UK product information says an anti-androgen tablet started three days before the first implant and continued for three weeks has been reported to prevent it.

Zoladex vs Prostap — is one better than the other?

Nobody has run a trial that would answer that. Prostap is leuprorelin, the other widely used drug of the same class, and no randomised comparison of the two for survival was found. A review that ranks goserelin above leuprolide for holding testosterone down is comparing results across separate trials in different patients, which is not the same thing, and the same review says the side effects are comparable between them. What does differ is the format: goserelin is a solid implant pushed under the skin through a wide needle, while leuprorelin is injected as a suspension, which is why people on the forums compare the two on what the injection itself is like rather than on survival.

Is Zoladex chemotherapy?

No. It is hormone treatment: it removes the hormone a tumour feeds on rather than attacking dividing cells. The clearest proof that they are different things is that one trial put them head to head — 1,640 premenopausal women got either two years of goserelin or six cycles of CMF chemotherapy — and the answer depended on the tumour. When it was driven by oestrogen, goserelin matched the chemotherapy. When it was not, the chemotherapy was clearly better.

Does Zoladex cause bone loss?

Yes, and it is the main reason courses are limited. After two years of treatment for early breast cancer, bone density had fallen by an average of 6.2% at the hip and 11.5% at the lower spine. For the non-cancer uses the product information puts it at about 1% a month, and says every 10% drop goes with roughly a two to three times higher chance of a fracture. Some of it comes back after stopping, but the label calls that recovery partial and says the figures behind it rest on very limited data — which is why it says repeat courses for endometriosis should not be given.

Does everything go back to normal after stopping Zoladex?

Periods usually come back within about eight weeks, and the labels still require non-hormonal contraception for twelve weeks after the last implant because ovulation can restart before that. Bone recovers only partly: a year after two years of treatment, the hip and spine were still 3.4% and 6.4% below where they started, on figures the product information itself calls very limited. And in the trial that compared goserelin with chemotherapy, three years after treatment ended 22.6% of the goserelin group still had no periods — against 76.9% of the chemotherapy group.

Can you buy goserelin online, and is it legal?

No, and it would not work if you could. It is not a liquid you can draw into a syringe — it is a solid implant that comes preloaded in a single-use applicator and has to be placed under the skin of the belly by a trained healthcare professional through a 16-gauge or 14-gauge needle. It is prescription-only wherever it is approved. In sport it is also banned: the 2026 World Anti-Doping Agency list names goserelin by name under section S2.2.1, among the testosterone-stimulating peptides prohibited in males.

Therapeutic

Goserelin

Also known as Zoladex · Zoladex LA · Zoladex 3.6 mg · Zoladex 10.8 mg · goserelin acetate · goserelin implant · ICI 118630 · ICI-118,630 · ZD-9393 · L02AE03 · Goserelina · Gosereline · Goserelinum · D-Ser(But)6,Azgly10-LHRH · goserlin

Approved medicine

21 of 51 peptides sit at this level

Category: Therapeutic
Doping status: Banned in sport
Sources: 16

Goserelin is a prescription medicine given as a small solid implant pushed under the skin of the belly, usually every four weeks or every twelve. It switches off the body's own sex-hormone signal, so testosterone in men or oestrogen in women falls to almost nothing. Approved since 1988 in Sweden and 1989 in the United States, it is used for prostate cancer, for breast cancer, for endometriosis, for fibroids and to thin the lining of the womb before an operation. Unusually for a drug this old, most of its trials had a real comparison group — surgery, another drug, or a dummy injection — so the numbers on this page mostly arrive with something to measure them against. The main long-term harm is bone loss, and the first few weeks carry a specific risk of the disease briefly getting worse.

GoserelinWhat it is

What it is
Sold and legal
In your body
What changed
What can go wrong
Amounts studied
What people say
Unknowns
Questions
Sources

What it is

A synthetic copy of GnRH, the hormone that tells the pituitary gland to switch the testicles or the ovaries on. It is a decapeptide — ten building blocks — but two of them are not ordinary amino acids: position 6 is a mirror-image serine carrying a bulky tert-butyl group, and position 10 is azaglycine, a glycine-like unit in which a nitrogen replaces the central carbon, capped with an amide. Neither can be written in the standard one-letter code, so the sequence field is deliberately left empty rather than filled with a string that would describe a different molecule. Both US labels print the structure as pyro-Glu-His-Trp-Ser-Tyr-D-Ser(But)-Leu-Arg-Pro-Azgly-NH2 and call it a synthetic decapeptide analogue of GnRH; PubChem gives C59H84N18O14 and 1,269.4 g/mol (CID 5311128), and the natural hormone it copies is ten residues long too (UniProt P01148, residues 24 to 33). Sold as Zoladex, it is not an injection of liquid at all: it is a solid cylinder about a millimetre across that is pushed under the skin of the lower belly and dissolves over 28 or 84 days.

How it is sold, and whether it is legal

Sold as: A solid biodegradable implant placed under the skin of the lower abdomen by a healthcare professional. It comes in two strengths, one replaced every 4 weeks and one every 12 weeks; the longer-acting implant is the larger of the two and goes in through a noticeably wider needle.
Legal status in the EU: An approved prescription medicine across the EU through national approvals rather than a single EU-wide one — there is no European Medicines Agency assessment report for Zoladex. In Sweden it was first approved on 17 June 1988 and the approval was renewed on 15 January 2009; the Swedish indications cover metastatic and locally advanced prostate cancer, adjuvant and neoadjuvant use with radiotherapy, advanced and adjuvant breast cancer, endometriosis, fibroids before surgery and thinning the lining of the womb. Banned in sport under the 2026 WADA list, section S2.2.1 on testosterone-stimulating peptides, which names goserelin among the GnRH agonist analogues — the ban applies to men only.

What it does in your body

7 parts of the body · all measured in people

Natural GnRH arrives in pulses; goserelin arrives constantly. So the first thing it does is the opposite of what it is for — the pituitary is stimulated, and testosterone in men or oestrogen in women rises before it falls. Held on without a break, the switch then jams shut. Testosterone reaches the level seen after surgical castration in about two to four weeks, and oestrogen reaches menopausal levels in about three. That first phase is why a tumour flare is a real early risk: in the controlled breast cancer trial it was recorded in 23 per cent of the 57 women on goserelin against 4 per cent of the 55 who had their ovaries removed instead, and in men the labels warn about a blocked tube from the kidney or pressure on the spinal cord. The UK product information says an anti-androgen tablet started three days before the first implant and continued for three weeks has been reported to prevent the consequences of that rise.

The hormone switch in the brain: A small gland under the brain, the pituitary, tells the testicles or the ovaries what to do, and it does it in pulses. Goserelin is a copy of that switch-on signal — which is why the first thing it does is the opposite of what it is for. In the first days the signal gets louder and testosterone in men, or oestrogen in women, goes up. Held on constantly instead of arriving in pulses, the switch then jams shut. In men, testosterone falls to the level seen in someone whose testicles have been removed after about two to four weeks, and stays there for as long as the implants continue. In women, oestrogen falls to the level of the menopause within about three weeks.; Stated in the pharmacology sections of both regulator labels, and confirmed against clinical trial follow-up of more than two years reported in the US label.; Measured in people; Source [01]Source [03]
Testicles, sex drive and erections, in men: With testosterone gone, sex drive usually goes with it and erections often stop. In the trials that compared the implant against having the testicles surgically removed, sexual difficulty was recorded in 21% of the 242 men on goserelin and 15% of the 254 men who had the operation, and reduced erections in 18% against 16%. Hot flushes were the most common effect in both groups. The UK product information lists reduced sex drive as very common, meaning more than 1 in 10 men, and lists breast tenderness and breast growth among the reported reactions.; Measured in 242 men on goserelin and 254 men who had their testicles removed, in the controlled trials behind the US label.; Measured in people; Source [01]Source [03]
Periods, the womb and the ovaries, in women: Oestrogen falls to menopausal levels and periods stop. In the two endometriosis trials, periods had stopped in 92% and 80% of all the women treated within eight weeks of the first implant. Some women bleed during the first two months before that happens; the label explains this as the bleeding that follows oestrogen being withdrawn and says it is expected to stop on its own. The womb and the lining of the womb shrink, which is the whole point of the use before an operation to remove that lining. Periods usually come back within about eight weeks of the last implant.; Measured in the two controlled endometriosis trials behind the US label, in which 411 women received goserelin and 207 received danazol, and in the placebo-controlled endometrial thinning trial in 358 women.; Measured in people; Source [01]
The ovaries during chemotherapy: Chemotherapy can shut the ovaries down permanently. Giving goserelin alongside it appears to protect them. Two years after treatment, the ovaries had failed in 5 of 66 women given goserelin with their chemotherapy (8%) and in 15 of 69 women given the chemotherapy alone (22%). More of the goserelin group later became pregnant: 22 of 105 against 12 of 113. This is not one of the approved uses on either the US or the UK label, and the American cancer society's own guideline calls the evidence conflicting and says the drug should not replace freezing eggs or embryos.; Measured in the POEMS/S0230 trial, which randomised 257 women with early hormone-receptor-negative breast cancer; 218 were eligible and evaluable and 135 of those had complete data for the main measurement.; Measured in people; Source [11]Source [12]Source [13]
Bones: Sex hormones are what keeps bone being rebuilt, so removing them thins it. This is the main harm of staying on the drug. After two years of treatment for early breast cancer, bone density had fallen by an average of 6.2% at the hip and 11.5% at the lower spine. For the non-cancer uses the product information puts the loss at about 1% a month over a six-month course, and states that every 10% drop in bone density goes with roughly a two to three times higher chance of breaking a bone. Some of it comes back afterwards, but the label calls that recovery partial and says the figures behind it rest on very limited data.; Reported in the UK and Swedish product information from the early breast cancer programme and from the treatment of non-cancer conditions. A separate US label figure comes from 109 women measured before and after six months of treatment, with no comparison group.; Measured in people; Source [01]Source [03]Source [04]
Blood sugar, weight and the heart: Blood sugar drifts up. Both labels tell doctors to check it periodically, because new diabetes and loss of control in existing diabetes are both reported with this class of drug in men. Weight gain is listed as a common reaction in both men and women. On the heart, the US label states that a raised risk of heart attack, sudden cardiac death and stroke has been reported with this class in men, adds that the risk appears low from the reported odds ratios, and asks prescribers to weigh it against a man's other heart risks. The one large randomised trial that followed men for ten years found no difference in deaths from heart causes between the men who had goserelin and the men who did not.; From the warnings sections of both regulator labels, which describe this as a class effect seen in men on GnRH agonists, and from the ten-year results of a trial that randomised 415 men.; Measured in people; Source [01]Source [03]Source [06]
The skin of the belly, where the implant goes: This is the part of goserelin that has no equivalent in a normal injection. The drug is not a liquid. It is a solid cylinder about a millimetre across, made of a material that slowly dissolves, and it is pushed under the skin of the lower belly through a wide needle — 16-gauge for the four-weekly implant, 14-gauge for the twelve-weekly one. It then sits there and releases the drug over 28 or 84 days. If it ever has to be taken out, the label says it can be found with an ultrasound scan. Reactions at the site were recorded in 3% of 242 men, against surgical complications in 18% of the 254 men who had the operation instead.; Described in sections 2, 3 and 16 of both US labels; the site-reaction figure comes from the controlled comparison of 242 men on goserelin against 254 men who had their testicles removed.; Measured in people; Source [01]Source [02]

What changed when it was measured

14 findings · 13 measured in people, 1 from one small study

Approved by the FDA on 29 December 1989 (NDA 019726, the 3.6 mg implant) and 11 January 1996 (NDA 020578, the 10.8 mg implant), and in Sweden on 17 June 1988. Its registration and follow-up trials nearly all carried a comparison group — surgical castration, removal of the ovaries, danazol, CMF chemotherapy or a dummy injection — rather than resting on single-arm hormone measurements. EORTC trial 22863 randomised 415 men with high-risk prostate cancer to radiotherapy with or without three years of goserelin: 58.1 per cent versus 39.8 per cent were alive at ten years (hazard ratio 0.60, 95% CI 0.45–0.80), and 10.3 per cent versus 30.4 per cent had died of the cancer. ZEBRA randomised 1,640 premenopausal women to two years of goserelin or six cycles of CMF chemotherapy and found them equivalent when the tumour was oestrogen-receptor-positive (HR 1.01, 95% CI 0.84–1.20) and goserelin inferior when it was not (HR 1.76, 95% CI 1.27–2.44). A placebo-controlled trial in 358 women found the lining of the womb measured 1.50 mm before surgery against 3.55 mm after dummy injections. Ovarian protection during chemotherapy is randomised evidence too (POEMS, ovarian failure 8 per cent versus 22 per cent) but is not an approved use on either label.

Days 1 to 14: the hormone the drug is meant to remove goes up first, and symptoms can briefly get worse. Weeks 2 to 4 in men: testosterone falls to the level seen after the testicles are removed and stays there while implants continue. About three weeks in women: oestrogen reaches menopausal levels. First two months in women: some bleed, which the label calls withdrawal bleeding and expects to stop on its own. Within eight weeks: periods had stopped in 92% and 80% of all treated women in the two endometriosis trials. Through the first six months: bone density falls at roughly 1% a month on the non-cancer uses. After the last implant, periods usually return within about eight weeks, but the labels still require non-hormonal contraception for twelve weeks. Bone comes back only partly — a year after two years of treatment for breast cancer, hip and spine were still 3.4% and 6.4% below where they started, on figures the product information itself calls very limited. Three years after treatment ended in the ZEBRA trial, 22.6% of the goserelin group were still without periods, against 76.9% of the chemotherapy group.

Being alive ten years after treatment for high-risk prostate cancer: 58.1% of the men who had radiotherapy plus three years of goserelin were alive at ten years, against 39.8% of the men who had the radiotherapy alone. The hazard ratio was 0.60, with a likely range from 0.45 to 0.80.; 415 men with locally advanced prostate cancer at high risk of it spreading, assigned by chance to one arm or the other, followed for a median of 9.1 years; Measured in people; Source [06]
Dying of prostate cancer within ten years: 10.3% of the men who had goserelin with their radiotherapy died of the cancer, against 30.4% of the men who had radiotherapy alone. The hazard ratio was 0.38, with a likely range from 0.24 to 0.60.; The same 415 men, ten years; Measured in people; Source [06]
Going ten years without the cancer coming back: 47.7% of the goserelin group were still free of clinical disease at ten years, against 22.7% of the radiotherapy-only group. The hazard ratio was 0.42, likely range 0.33 to 0.55.; The same 415 men, ten years; Measured in people; Source [06]
The cancer coming back where it started, after radiotherapy: 16% of the men given goserelin and flutamide before and during radiation had the cancer return locally within four years, against 33% of the men given radiation alone. Median time before the disease came back was 4.4 years against 2.6 years.; 466 men with bulky tumours confined to the prostate or extending just beyond it: 231 on the combination and 235 on radiation alone; Measured in people; Source [01]
Goserelin instead of chemotherapy, in premenopausal breast cancer: In the women whose tumours were driven by oestrogen, two years of goserelin came out the same as six cycles of CMF chemotherapy for keeping the disease away: hazard ratio 1.01, likely range 0.84 to 1.20. In the women whose tumours were not driven by oestrogen, goserelin was clearly worse than the chemotherapy: hazard ratio 1.76, likely range 1.27 to 2.44.; 1,640 premenopausal women with breast cancer that had reached the lymph nodes: 817 given goserelin and 823 given CMF chemotherapy, median follow-up 6 years; Measured in people; Source [07]Source [14]
Whether periods come back, after goserelin or after chemotherapy: More than 95% of the goserelin group had stopped having periods by six months, against 58.6% of the chemotherapy group. Three years after treatment ended the picture had reversed: 22.6% of the goserelin group were still without periods, against 76.9% of the chemotherapy group.; The same 1,640 women in the ZEBRA trial; Measured in people; Source [07]
Ovarian failure two years after chemotherapy: The ovaries had failed in 5 of 66 women who had goserelin alongside their chemotherapy (8%) and in 15 of 69 women who had the chemotherapy alone (22%). The odds ratio was 0.30, with a likely range from 0.09 to 0.97.; Women with early hormone-receptor-negative breast cancer in the POEMS/S0230 trial; 257 were randomised, 218 were eligible and evaluable, and 135 of those had complete data for this measurement; Measured in people; Source [11]
Becoming pregnant after chemotherapy: 22 of the 105 women in the goserelin group had at least one pregnancy (21%), against 12 of the 113 women in the chemotherapy-alone group (11%).; The 218 evaluable women in the POEMS/S0230 trial; Measured in people; Source [11]
Ovarian protection, pooled across every randomised trial of the class: Early ovarian failure happened to 14.1% of the women given a GnRH agonist during chemotherapy and 30.9% of the women given chemotherapy alone, adjusted odds ratio 0.38. Pregnancies afterwards: 10.3% against 5.5%. Living longer was not shown — the hazard ratio for staying free of disease was 1.01 and for overall survival 0.67, and neither reached statistical significance.; 873 premenopausal women with early breast cancer, pooled patient by patient from five randomised trials, of which POEMS is the goserelin one; Measured in people; Source [15]
Shrinking endometriosis lesions, against the older drug it replaced: In the first trial, 63% of the women on goserelin and 42% of the women on danazol had their lesions shrink by at least half. In the second, it was 62% against 51%. The label adds that what a shrinking lesion means for a person is not known, and that the surgical staging of endometriosis does not necessarily track how bad the symptoms are.; Two controlled trials of the four-weekly implant over six months; 411 women received goserelin and 207 received danazol across the safety dataset; Measured in people; Source [01]
Periods stopping after an operation to remove the lining of the womb: Six months after the operation, 70 of 175 women who had been given two goserelin implants first had no periods at all (40%), against 44 of 171 who had been given dummy injections (26%). Before the operation, the lining of the womb measured 1.50 mm in the goserelin group against 3.55 mm in the placebo group.; 358 premenopausal women with heavy or irregular bleeding, assigned by chance and with neither they nor their doctors told which they had; 180 had goserelin and 178 had placebo injections; Measured in people; Source [01]
The twelve-weekly implant against three four-weekly ones: PSA — the blood marker used to follow prostate cancer — fell by 94% on the twelve-weekly implant and 92.5% on the four-weekly one at three months, and average testosterone suppression was similar. The label says only that a similar clinical outcome is predicted; survival was not compared.; 160 men with advanced prostate cancer across two controlled trials, three months; Measured in people; Source [02]
Bone at the lower spine over a six-month course: Bone density fell by an average of 4.3% over six months. There was no comparison group — the women were measured against their own readings from before treatment. Six months after finishing, 66 of them were still 2.4% below where they started, and twelve months after finishing, 28 of them were still 2.5% below.; 109 women treated for six months with the four-weekly implant; Measured in people; Source [01]
Goserelin instead of having the ovaries removed, in advanced breast cancer: On interim data, tumours responded in 22% of the goserelin group and 12% of the group who had the operation. Median survival was 33.2 months against 33.6 months, and roughly half of each group said they felt better on measures of pain and daily functioning: 48% against 50%.; 124 premenopausal women with advanced hormone-receptor-positive breast cancer in SWOG-8692, assigned by chance to goserelin or to surgical removal of the ovaries; One small study; Source [01]

What can go wrong

14 effects, 8 serious

Hot flushes and sweats are the most common effect and beat every comparison group they were measured against: 62 per cent of 242 men on goserelin versus 53 per cent of 254 men who had their testicles removed, and 96 per cent of 411 women with endometriosis versus 67 per cent of 207 on danazol. The initial hormone rise can make the disease briefly worse. Long-term use thins bone — 6.2 per cent at the hip and 11.5 per cent at the lower spine after two years of breast cancer treatment, and about 1 per cent a month on the six-month non-cancer courses, where the product information puts every 10 per cent drop at roughly a two to three times higher fracture risk. The labels also warn about severe skin reactions including Stevens-Johnson syndrome, raised blood sugar and new diabetes, heart attack, heart failure and stroke in men, too much calcium in the blood in people whose cancer has reached the bones, and injury where the wide needle goes in, up to haemorrhagic shock needing transfusion and surgery.

The disease briefly getting worse after the first implantSerious: For the first days after the first implant the hormone the drug is meant to remove goes up instead of down, because goserelin copies the signal that switches the sex glands on. Symptoms can briefly worsen: more bone pain, and in men trouble passing urine, a blocked tube from the kidney or, at worst, pressure on the spinal cord. The UK product information says an anti-androgen tablet, cyproterone acetate 300 mg daily for three days before and three weeks after the first implant, has been reported to prevent the consequences of that rise. Symptoms usually settle as treatment continues.; 23% of the 57 women with advanced breast cancer in the controlled trial, against 4% of the 55 women who had their ovaries removed instead. In men the labels describe it without a percentage, as something a small proportion experience.; Source [01]Source [03]
Bleeding or injury where the implant goes inSerious: This one belongs to the implant rather than the drug. The needle is wide, and the label reports pain, bruising, bleeding and, at the far end, haemorrhagic shock needing a blood transfusion and an operation. The label tells prescribers to take extra care in people who are very slim or on full-dose blood thinners, to check for blood appearing in the syringe chamber, and not to push the needle into muscle or into the abdominal cavity.; No rate. These were reported after the drug was already on the market, so nobody knows how often they happen. Ordinary reactions at the site were recorded in 3% of 242 men in the trials.; Source [01]
Broken bones from thinned boneSerious: Bone loss is why the endometriosis course is capped at six months and why the UK product information says repeat courses should not be given. It also notes that there are no specific data for people who already have thin bones or who carry the risk factors for it — heavy drinking, smoking, long-term steroids or anti-epileptic drugs, a family history, or an eating disorder — and that the loss is likely to matter more in those people.; No fracture rate is given for goserelin itself. The product information puts bone loss at about 1% a month over a six-month course and states that every 10% drop in bone density goes with about a two to three times higher fracture risk.; Source [01]Source [03]Source [04]
Severe skin reactions that strip the skinSerious: Stevens-Johnson syndrome and toxic epidermal necrolysis are reactions in which the skin blisters and peels; two related reactions are also named. They can be life-threatening or fatal, and some reported cases involved internal organs or needed skin grafts. The label tells prescribers to stop the drug while the cause is worked out and to stop it permanently if the diagnosis is confirmed.; Frequency not known. Reported after the drug was already on the market, and too rare to have shown up in the trials.; Source [01]
Ovarian hyperstimulation, when it is used as part of fertility treatmentSerious: The ovaries swell and fluid leaks into the abdomen. It causes bloating, pain, sickness and, in the severe form, breathing difficulty and blood clots. It is a risk of the fertility use rather than of the cancer or endometriosis uses.; Rare in the UK product information, meaning between 1 in 10,000 and 1 in 1,000, and reported only in combination with the gonadotrophin injections used in assisted reproduction.; Source [03]
A tumour or a bleed in the pituitary glandSerious: The pituitary is the gland under the brain that goserelin acts on. A bleed into it causes sudden severe headache, vomiting, vision changes and confusion, and needs immediate medical attention.; Very rare in the UK product information, meaning fewer than 1 in 10,000. Psychotic illness is listed at the same frequency.; Source [03]
Too much calcium in the bloodSerious: It causes thirst, needing to pass urine often, sickness, confusion and weakness, and it needs treating. It is listed as an uncommon reaction in women in the UK product information.; No rate given. Reported in people whose prostate or breast cancer had already spread to the bones, after starting treatment.; Source [01]Source [03]
Heart failure, heart attack and strokeSerious: The US label states that a raised risk of heart attack, sudden cardiac death and stroke has been reported with this class of drug in men, that the risk appears low from the reported odds ratios, and that it should be weighed against a man's other heart risks. The UK product information adds that the risk appears higher when the drug is combined with an anti-androgen. The one trial that followed men for ten years found no difference in deaths from heart causes. The drug can also lengthen the heart's electrical recovery time, which matters for anyone already on medicines that do the same.; Heart failure was recorded in 5% of the 242 men on goserelin and 1% of the 254 men who had their testicles removed, in the old controlled comparison behind the US label. Heart failure and heart attack are both listed as common in men in the UK product information, meaning between 1 in 100 and 1 in 10.; Source [01]Source [03]Source [06]
Hot flushes and sweats: A sudden feeling of heat in the face, neck or chest, often with sweating. Both product information sheets class it as very common, meaning more than 1 in 10. The US label notes that adding hormone replacement alongside goserelin appeared in studies to reduce flushes and vaginal dryness without blunting its effect on pelvic symptoms, but says the best drug, dose and duration have not been established.; The most common effect by a distance, and it beat every comparator it was measured against: 62% of 242 men on goserelin versus 53% of 254 men who had their testicles removed; 96% of 411 women with endometriosis versus 67% of 207 on danazol; 70% of 57 women with breast cancer versus 47% of 55 who had their ovaries removed. In the endometrial thinning trial, flushing was recorded in 57% of 180 women on goserelin against 18% of 177 on dummy injections.; Source [01]Source [03]
Loss of sex drive, and dryness or discomfort during sex: These follow directly from removing the sex hormones and they last as long as treatment does. Both product information sheets list reduced sex drive and vaginal dryness among the very common reactions.; In men, sexual difficulty in 21% of 242 against 15% of 254 who had the operation. In women with endometriosis, reduced sex drive in 61% of 411 against 44% of 207 on danazol, inflammation or dryness of the vagina in 75% against 43%, and pain during sex in 14% against 5%.; Source [01]Source [03]
Low mood and swings in mood: The US label carries a specific instruction about this: watch women for depression, especially anyone with a history of it, weigh up whether to continue, and refer anyone whose mood is getting worse. Memory problems appear separately, with no known frequency.; In the endometriosis trials, depression in 54% of 411 women on goserelin against 48% of 207 on danazol, and mood swings in 60% against 56%. Both product information sheets list mood change and depression as common in men and in women.; Source [01]Source [03]
Headache: Common enough in both arms of both trials that the drug clearly adds to it rather than causing all of it. Migraine was also more common on goserelin in the endometrial thinning trial, 7% against 4%.; 75% of 411 women with endometriosis against 63% of 207 on danazol. In the endometrial thinning trial, 32% of 180 women on goserelin against 22% of 177 on dummy injections.; Source [01]
Bleeding in the first two months, in women: It is the bleeding that follows oestrogen being withdrawn, and the label says it is expected to stop on its own. It surprises people, because the drug is supposed to stop periods.; No percentage given. The label describes it as something some women experience during the first two months of use, of variable duration and intensity.; Source [01]
Weight gain: The trial figure is the one place where goserelin came out far better than what it was compared against, because danazol is a hormone drug that causes weight gain in its own right. It is not a reason to read 3% as the rate people should expect.; Listed as common in both men and women in the UK product information, meaning between 1 in 100 and 1 in 10. In the endometriosis trials, weight gain was recorded in 3% of 411 women on goserelin against 23% of 207 on danazol.; Source [01]Source [03]

Who it is known to be dangerous for

Anyone who is pregnant or breastfeeding: the UK product information makes both an absolute contraindication, and the US label allows it in pregnancy only for the palliative treatment of advanced breast cancer, where the doctor must warn the patient about the risk to the baby. Any woman with vaginal bleeding that has not been explained yet. Anyone who has reacted badly before to this drug, to GnRH itself or to another drug of the same family — anaphylactic reactions have been reported. Premenopausal women using it must use non-hormonal contraception during treatment and for twelve weeks afterwards, because it usually stops ovulation but does not reliably prevent pregnancy. Men at particular risk of a blocked tube from the kidney or of pressure on the spinal cord need careful thought and close watching through the first month, because of the initial hormone rise. Extra care is needed in anyone very slim or on full-dose blood thinners, because of bleeding where the needle goes in. There are no specific data in people who already have thin bones or the risk factors for them, and none in children.

The amounts the studies used

7 amounts

These are the amounts the studies below gave their participants, and they are here as facts about those studies. They are not a recommendation, not a starting point and not a range to pick from. What a person should take, if anything, is a question for a doctor who knows them.

EORTC trial 22863, radiotherapy with or without long-term hormone suppression, in men with locally advanced prostate cancer at high risk of it spreading: 3.6 mg implant under the skin every four weeks, started on the first day of irradiation; Three years, in 207 of the 415 men; Source [06]
The US Stage B2-C trial of hormone treatment plus radiation, in men with bulky tumours confined to the prostate or just beyond it: 3.6 mg implant plus flutamide 250 mg three times a day, starting eight weeks before radiation and continuing through it; Through the radiation course, in 231 of the 466 men; Source [01]
The two controlled trials comparing the two implant sizes, in men with advanced prostate cancer: 10.8 mg implant under the skin every twelve weeks, or 3.6 mg every four weeks; Three months, in 160 men; Source [02]
The ZEBRA trial, goserelin against CMF chemotherapy, in premenopausal women with breast cancer that had reached the lymph nodes: 3.6 mg implant every 28 days; Two years, in 817 women; Source [07]
POEMS/S0230, protecting the ovaries during chemotherapy, in women with early hormone-receptor-negative breast cancer: 3.6 mg implant every four weeks, starting one week before the chemotherapy; For as long as the chemotherapy lasted, in 105 evaluable women; Source [11]Source [12]
The two controlled endometriosis trials that the US approval rests on, against danazol: 3.6 mg implant every 28 days; Six months, in 411 women; Source [01]
Trial 0022, thinning the lining of the womb before an operation to remove it, in premenopausal women with heavy or irregular bleeding: Two 3.6 mg implants given four weeks apart, or two dummy injections; About six weeks before surgery, in 358 women; Source [01]

What people report

What follows is what people say online. It is not evidence, it is not graded, and it is not checked by anyone. People who had a bad time and people who are selling something both post more than people for whom nothing happened. It is here because you would go and read it anyway, and knowing who is talking is better than not.

Whether the implant hurts depends almost entirely on who is giving it

A thread on the Prostate Cancer UK community started in August 2015 by a man whose injection was given by an unfamiliar nurse without numbing spray drew around 20 replies in three days. He wrote that he had the most unbearable pain and that people in the waiting room heard him scream. Several repliers said the opposite about the same drug: one had had seven three-monthly implants using freeze spray, all of them totally pain free. Others recommended numbing cream, and one suggested switching to a different drug of the same class, on the stated grounds that it is a fluid injection rather than a pellet. The original poster checked with his GP and a Macmillan nurse, was told the implant would still work, and went back to his usual nurse.

Read in Prostate Cancer UK Online Community, Advanced or metastatic cancer board, thread unbearable zoladex injection, around 20 replies from August 2015

What the published studies say

The regulator label records reactions at the injection site in 3% of 242 men, and separately warns — with no frequency at all — about injection site and vascular injury up to haemorrhagic shock needing transfusion and surgery. Neither number tells you anything about whether a particular nurse will use freeze spray.

People disagree about whether the flushes spike right after each implant

In a short thread on the Breast Cancer Now forum from February 2022, one woman seven months into goserelin and an aromatase inhibitor described hot flushes, brain fog, joint aches and low energy, and suspected her flushes got worse for a week or so after each injection. The only replier reported the same symptoms but said she could not say she flushed more after the implant, and put hers down to caffeine and to the time of night. Both accepted the side effects as the price of treatment.

Read in Breast Cancer Now forum, Hormone therapy board, thread Zoladex side effects, two posts on 10 February 2022

What the published studies say

The trials counted only whether a flush happened at all — 70% of 57 women against 47% of the women who had their ovaries removed instead. Nothing in the published record measures whether flushes cluster in the days after an implant, which is the exact question both women were asking.

Bleeding after starting is common enough online to surprise both patients and doctors

A Cancer Research UK Cancer Chat thread with eleven replies was started by a woman who had a heavy period after starting goserelin, which surprised her because chemotherapy had already stopped her periods. Another woman in the thread reported unexpected bleeding too and said her oncologist seemed puzzled by it. Others in the thread discussed why goserelin and tamoxifen are given together, one describing her oncologist's explanation as belt and braces, and one poster mentioned being four and a half years in with six to go.

Read in Cancer Research UK Cancer Chat, Moving on board, thread Zoladex injection for breast cancer, 11 replies

What the published studies say

The label already says this: during the first two months some women bleed, of variable duration and intensity, most likely because oestrogen has been withdrawn, and it is expected to stop on its own. It is written down and it still catches people out.

Where to read it yourself

Prostate Cancer UK Online Community
Forum
A discussion board run by the UK charity Prostate Cancer UK, with separate boards for side effects and for advanced disease, and a specialist nurse phone line reachable from the same site.
Almost everyone posting is a man with a prostate cancer diagnosis or his partner, mostly older and mostly in the UK. Nobody is selling anything, but nothing posted is checked for accuracy. Men whose treatment is going quietly have little reason to start a thread, so the board over-represents the ones having a hard time.
Breast Cancer Now forum
Forum
The discussion forum of the UK charity Breast Cancer Now, with boards organised by treatment type, including one for hormone therapy where goserelin comes up constantly.
The posters are people going through breast cancer treatment, overwhelmingly women, overwhelmingly UK-based. Threads are often two or three posts long, so a pattern seen there rests on a handful of people, not a survey. The charity moderates but does not fact-check.
Cancer Research UK Cancer Chat
Forum
A moderated public forum run by Cancer Research UK, organised by stage of the experience rather than by cancer type, with boards such as living with cancer and moving on.
Open to anyone, including people writing about a relative rather than themselves, so posts mix first-hand and second-hand accounts. Threads stay open for years, which means replies can come from a very different point in treatment than the original question.
MHRA Yellow Card interactive Drug Analysis Profiles
Official side-effect reports
The UK regulator's published listing of suspected side effects reported to it, organised by the name of the active substance rather than the brand name.
A report only means somebody suspected a link; the regulator states this is not proof the medicine caused anything, and asks that the data be read alongside its own guidance at the foot of each report. There is no denominator, so you cannot work out how often anything happens, and there is about a month between a report arriving and appearing.

What nobody has measured

13 unknowns

Whether goserelin differs from the other drugs of its class for survival. No randomised trial comparing it head to head with leuprorelin was found; the review that ranks it above leuprolide for holding testosterone down compares results across separate trials in different patients.
Whether the twelve-weekly implant gives the same clinical outcome as three four-weekly ones. The label says a similar outcome is predicted, on 160 men measured by testosterone and PSA over three months, not by survival.
Whether protecting the ovaries during chemotherapy is safe when the breast tumour is driven by oestrogen. The goserelin trial enrolled only women whose tumours were not, and the pooled analysis of the whole class found no survival benefit either way.
Whether more women end up with the family they wanted. The pregnancy figures come from trials built to measure a hormone-defined definition of ovarian failure, and in the goserelin trial only 135 of the 218 evaluable women had complete data for even that.
How much bone comes back after stopping. The product information calls the recovery partial and states outright that the recovery figures rest on very limited data.
What happens to bone in men on goserelin for years. Neither label gives a bone figure for men — osteoporosis, reduced bone density and fracture in men appear only in the list of things reported after marketing.
How often the initial hormone rise causes real harm in men. Both labels describe blocked kidney tubes and pressure on the spinal cord as isolated cases, with no rate attached.
How often the injection-site bleeding happens. Haemorrhage, haemorrhagic shock, transfusion and surgery are all named in the warnings, and all of them come from reports made after the drug was on the market, with no denominator.
Whether the heart signal is caused by the drug. The label calls it a class association from a pharmaco-epidemiology study and says the risk appears low from the reported odds ratios; the one trial that followed men for ten years found no difference in deaths from heart causes.
What it does to memory and thinking. Memory impairment is listed with no known frequency, and none of the randomised trials measured it.
Whether a second course for endometriosis is safe. The product information says repeat courses should not be given because of bone, and that there are no clinical data for treatment beyond six months.
What it does in people who already have thin bones or the risk factors for them. The product information states plainly that there are no specific data for those patients.
Anything at all in children. Goserelin has no paediatric indication anywhere, and no paediatric trial data appears in either label — unlike leuprorelin, which is approved for puberty that starts far too early.

Questions people ask

8 questions

Does Zoladex actually work?: For the things it is approved for, yes, and the evidence is unusually solid because its trials had real comparison groups. In men with high-risk prostate cancer, adding three years of goserelin to radiotherapy left 58.1% alive at ten years against 39.8% on radiotherapy alone. In women with endometriosis it shrank lesions in 63% against 42% on the older drug danazol. In premenopausal breast cancer it matched chemotherapy when the tumour was driven by oestrogen — and was clearly worse than chemotherapy when it was not.; Source [01]Source [06]Source [07]
What are the side effects of Zoladex?: Hot flushes and sweats are by far the most common, and they beat every comparison group they were tested against: 62% of men on goserelin versus 53% of men who had their testicles removed, and 96% of women with endometriosis versus 67% on danazol. Loss of sex drive, low mood, headache and weight gain are all common. The one that matters most over time is bone loss, at about 1% a month on a six-month course. The rare but serious list includes skin reactions that strip the skin, bleeding where the implant goes in, and too much calcium in the blood in people whose cancer has reached the bones.; Source [01]Source [03]
Does Zoladex make the cancer worse at first?: Briefly, and this is the strangest thing about the drug. Goserelin is a copy of the natural signal that switches the sex glands on, so the first implant pushes the hormone up before the switch jams shut. In the controlled breast cancer trial, this tumour flare was recorded in 23% of the 57 women on goserelin and 4% of the 55 who had their ovaries removed instead. In men it can mean a few weeks of worse bone pain or urinary trouble and, rarely, pressure on the spinal cord. The UK product information says an anti-androgen tablet started three days before the first implant and continued for three weeks has been reported to prevent it.; Source [01]Source [03]
Zoladex vs Prostap — is one better than the other?: Nobody has run a trial that would answer that. Prostap is leuprorelin, the other widely used drug of the same class, and no randomised comparison of the two for survival was found. A review that ranks goserelin above leuprolide for holding testosterone down is comparing results across separate trials in different patients, which is not the same thing, and the same review says the side effects are comparable between them. What does differ is the format: goserelin is a solid implant pushed under the skin through a wide needle, while leuprorelin is injected as a suspension, which is why people on the forums compare the two on what the injection itself is like rather than on survival.; Source [01]Source [16]
Is Zoladex chemotherapy?: No. It is hormone treatment: it removes the hormone a tumour feeds on rather than attacking dividing cells. The clearest proof that they are different things is that one trial put them head to head — 1,640 premenopausal women got either two years of goserelin or six cycles of CMF chemotherapy — and the answer depended on the tumour. When it was driven by oestrogen, goserelin matched the chemotherapy. When it was not, the chemotherapy was clearly better.; Source [01]Source [07]
Does Zoladex cause bone loss?: Yes, and it is the main reason courses are limited. After two years of treatment for early breast cancer, bone density had fallen by an average of 6.2% at the hip and 11.5% at the lower spine. For the non-cancer uses the product information puts it at about 1% a month, and says every 10% drop goes with roughly a two to three times higher chance of a fracture. Some of it comes back after stopping, but the label calls that recovery partial and says the figures behind it rest on very limited data — which is why it says repeat courses for endometriosis should not be given.; Source [03]Source [04]
Does everything go back to normal after stopping Zoladex?: Periods usually come back within about eight weeks, and the labels still require non-hormonal contraception for twelve weeks after the last implant because ovulation can restart before that. Bone recovers only partly: a year after two years of treatment, the hip and spine were still 3.4% and 6.4% below where they started, on figures the product information itself calls very limited. And in the trial that compared goserelin with chemotherapy, three years after treatment ended 22.6% of the goserelin group still had no periods — against 76.9% of the chemotherapy group.; Source [01]Source [07]
Can you buy goserelin online, and is it legal?: No, and it would not work if you could. It is not a liquid you can draw into a syringe — it is a solid implant that comes preloaded in a single-use applicator and has to be placed under the skin of the belly by a trained healthcare professional through a 16-gauge or 14-gauge needle. It is prescription-only wherever it is approved. In sport it is also banned: the 2026 World Anti-Doping Agency list names goserelin by name under section S2.2.1, among the testosterone-stimulating peptides prohibited in males.; Source [01]Source [09]

Sources

16 sources

Cancer care · Hormones

18 peptides · strongest evidence first