What is degarelix used for?

It treats prostate cancer that feeds on testosterone — advanced disease, and higher-risk disease that is still confined or locally spread, where it is given before or alongside radiotherapy. It works by shutting testosterone down to the level a man would have after having his testicles removed. It is sold as Firmagon and given as an injection under the skin of the abdomen by a nurse or doctor.

For the job it is licensed to do, yes. In the trial behind its approval, 97.2% of the men on degarelix held testosterone at the castration level from day 28 through the whole year, against 96.4% of the men on monthly leuprorelin — the same, not better. What is different is the speed: 96% of the degarelix group were there by day 3 against nobody in the other group. No trial has shown that men live longer on degarelix than on the older injections.

Degarelix vs Lupron — what is the actual difference?

Lupron and its relatives switch the hormone signal on hard before exhausting it, so testosterone spikes for the first week and then falls over three to four weeks; degarelix blocks the same switch directly, so there is no spike and testosterone is down within days. That means no anti-androgen tablet is needed as cover at the start. After the first month the two are equivalent on testosterone and PSA. The trade-offs are practical: degarelix is a monthly injection that leaves a sore lump in about a third of men, while the agonists can be given every three or six months and almost never do.

Is degarelix better for the heart than the older injections?

Nobody knows, and this is the most important thing on this page. The idea came from a re-analysis of six old trials, done after the fact, which found about half as many cardiac events on degarelix in men who already had heart disease — its own authors called that hypothesis-generating. A trial called PRONOUNCE was then built to test it properly and could not finish: it stopped at 545 men of the 900 planned, and reported heart events in 5.5% of the degarelix group against 4.1% of the leuprolide group, a difference that could easily be chance. Pooling everything published up to the end of 2023 gives no difference either.

What are the side effects of degarelix?

The common ones are a red painful lump where the needle went in, in about a third of men; hot flushes in a quarter; and raised liver enzymes on a blood test in one in ten. Shrunken testicles, loss of erections, breast growth, tiredness and weight change follow from having no testosterone and continue for as long as treatment does. Rare but serious problems include severe allergic reactions, an infected or broken-down injection site, and heart rhythm trouble.

Does degarelix weaken your bones?

Probably, but it was never measured. Thinning bone and osteoporosis appear on the reaction list in the uncommon band, and taking testosterone away is known to thin bone in men who have had their testicles removed or taken the older drugs. The EU product information states in one flat sentence that bone density has not been measured during treatment with degarelix, which after more than fifteen years on the market is a striking gap.

How long does degarelix take to work?

Faster than anything else in its class. Half of the men in the trial were at the castration testosterone level within one day, 96% within three days and everyone within a month. PSA, the blood marker used to follow the cancer, was down 64% at two weeks, 85% at one month and 95% at three months. Coming off it is slow in the other direction: testosterone took a median of 112 days to climb back above the castration level.

Is degarelix banned in sport?

It does not appear on the 2026 World Anti-Doping Agency Prohibited List. The relevant section, S2.2.1, bans testosterone-stimulating peptides in men and names the hormone GnRH together with its agonist copies — goserelin, leuprorelin, triptorelin and others. Degarelix is the opposite kind of molecule, an antagonist that blocks the same receptor and lowers testosterone rather than raising it, and the word degarelix does not appear anywhere in the document.

Therapeutic

Degarelix

Also known as Firmagon · Firmagon 80 mg · Firmagon 120 mg · degarelix acetate · Degarelixum · FE 200486 · FE200486 · CAS 214766-78-6 · ATC L02BX02 · NDA 022201 · GnRH antagonist (prostate cancer) · LHRH antagonist injection · Ac-D-2Nal-D-4Cpa-D-3Pal-Ser-4Aph(Hor)-D-4Aph(Cbm)-Leu-ILys-Pro-D-Ala-NH2 · degarelex · degarilix · firmagom

Approved medicine

21 of 51 peptides sit at this level

Category: Therapeutic
Doping status: Not banned in sport
Sources: 14

Degarelix is a prescription medicine for advanced prostate cancer, injected under the skin of the belly by a nurse or doctor, never bought or self-administered. It shuts off testosterone by blocking the pituitary switch directly, which is the opposite of how the older drugs of this kind work: there is no first-week hormone surge, and testosterone reaches the target level in days rather than weeks. Over a year, its testosterone results matched monthly leuprorelin almost exactly, and the price of the faster start is a painful red lump where the needle went in, in about a third of men against under 1 in 100 on the older injection. The heart advantage degarelix is often credited with was put to a trial called PRONOUNCE, which stopped early with too few participants to answer the question, and reported slightly more heart events on degarelix rather than fewer.

DegarelixWhat 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 ten-amino-acid chain that blocks the brain's sex-hormone switch instead of overstimulating it, sold as Firmagon and injected under the skin of the abdomen for prostate cancer. The US label describes it as a linear decapeptide amide containing seven unnatural amino acids, five of them mirror-image D-forms, plus an amide cap. None of that 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. PubChem gives C82H103ClN18O16 and 1,632.3 g/mol.

How it is sold, and whether it is legal

Sold as: Injection under the skin of the abdomen, given by a healthcare professional: a larger loading amount split across two injections on the first visit, then a smaller one once a month.
Legal status in the EU: Approved EU-wide as Firmagon (Ferring Pharmaceuticals A/S) on 17 February 2009, most recently renewed 13 November 2013, and in the US as NDA 022201 on 24 December 2008. Prescription only, given by a healthcare professional; the product information says it is for injection under the skin only, never into a vein, and that injection into muscle has not been studied. Degarelix does not appear on the 2026 WADA Prohibited List. Section S2.2.1 bans testosterone-stimulating peptides in men — GnRH and its agonist analogues, naming goserelin, leuprorelin and triptorelin among others — and degarelix is an antagonist that lowers testosterone rather than raising it.

What it does in your body

11 parts of the body · 9 measured in people, 2 claimed but never tested

The pituitary gland releases two hormones that tell the testicles to make testosterone, and it does so on a signal called GnRH. Goserelin and leuprorelin are copies of that signal: they switch the receptor on hard, testosterone spikes for a week, and only then does the switch jam shut. Degarelix does the opposite — it sits on the same receptor and blocks it, the way a key that fits but will not turn blocks a lock. Nothing is switched on first, so there is no hormone surge and no tumour flare, and testosterone falls in days rather than weeks. The binding is competitive and reversible, so the effect lasts only as long as the monthly depot keeps releasing drug.

The hormone switch in the brain: A small gland under the brain, the pituitary, releases two signalling hormones that tell the testicles to make testosterone. Degarelix sits on the receptor those signals come from and blocks it, the way a key that fits but will not turn blocks a lock. Because nothing is switched on first, the signalling hormones and then testosterone start falling immediately. Half of the men were at the castration level of 0.5 nanograms per millilitre within one day and 96% within three days; on monthly leuprorelin, which switches the same receptor on before it exhausts it, nobody was there at day 3 and 18% by day 14. Both drugs had everyone there by day 28.; Measured on days 1, 3, 7, 14 and 28 in 207 men on the approved degarelix dose and 201 men on monthly leuprorelin 7.5 mg, inside a 620-man randomised trial.; Measured in people; Source [01]Source [02]
The first week, and the flare that does not happen: With the older drugs of this class, the first injection pushes testosterone up before it pulls it down, and in a man with prostate cancer that brief rise can make bone pain, urinary trouble or pressure on the spine worse. Degarelix does not do this. In the trial, a surge was defined as testosterone going at least 15% above where it started within the first two weeks; not one man on degarelix had one, and testosterone was down an average of 94% by day 3, while most men on leuprorelin had a surge and averaged 65% above their starting level on the same day. That is why no anti-androgen tablet is added as cover when degarelix is started.; Measured in the same 620-man randomised trial; the difference between the two arms at day 3 was statistically significant, at p below 0.001.; Measured in people; Source [01]Source [05]
Where the needle goes in, on the belly: The powder is mixed with liquid and injected into the fat of the abdomen, where it sets into a depot that releases the drug over the following month. That depot is felt. Pain was recorded in 28% of men and redness in 17%, with swelling in 6%, hardening in 4% and a lump in 3%. Almost all of it comes with the big starting dose; once men are on the monthly 80 mg dose the rate falls to about 3 episodes of pain per 100 injections and under 1 per 100 for everything else. On the comparison injection into muscle, injection site reactions were recorded in under 1% of men.; Recorded in 207 men on degarelix and 201 on monthly leuprorelin over 12 months, and counted per injection during the maintenance phase.; Measured in people; Source [01]Source [02]
Testicles, sex drive and breasts: Once testosterone is gone the testicles shrink, erections usually stop and sex drive falls. The EU product information lists shrunken testicles, erectile difficulty and breast growth as common, meaning more than 1 in 100 men and fewer than 1 in 10, and lists reduced sex drive as uncommon, between 1 in 1,000 and 1 in 100. Fertility is suppressed for as long as testosterone is. None of this is specific to degarelix — it is what happens whenever testosterone is taken away.; Pooled from 1,259 patients treated for a total of 1,781 patient-years across the phase 2 and phase 3 studies, plus post-marketing reports.; Measured in people; Source [01]Source [02]
The prostate, and the PSA blood test: PSA is a protein made by the prostate and measured in blood to follow the cancer. It fell by 64% two weeks after the first degarelix injection, 85% after a month and 95% after three months, and stayed down at about 97% for the rest of the year. In the first month those falls were steeper than on leuprorelin, but from day 56 onwards the two arms were no different. The prostate itself shrinks: three months of degarelix before radiotherapy reduced prostate volume by 36.0%, against 35.3% with goserelin plus an anti-androgen tablet.; Measured through 12 months in the 620-man randomised trial, and over 12 weeks in a separate randomised trial of 244 men due to have radiotherapy.; Measured in people; Source [01]Source [02]Source [10]
The liver: Liver enzymes drift up on degarelix more often than on the comparison injection: raised transaminases and GGT were recorded in 10% of men against 5%. They are usually mild, usually reversible, and are not accompanied by a rise in bilirubin or by symptoms. In the long extension study, where men stayed on the drug for a median of about 43 months, mild or moderate enzyme rises were recorded in 47% and severe ones in 1%.; Measured over 12 months in 207 men against 201 on leuprorelin, then over a median of roughly 43 months in 385 men with no comparison group.; Measured in people; Source [01]Source [02]
The heart's electrical timing: Blocking testosterone lengthens the heart's electrical recovery time, called the QT interval, which matters for anyone already on medicines that do the same. In the trial about 20% of men in both arms went past 450 milliseconds. Going past 500 milliseconds, the level that worries cardiologists most, happened in 3 of 409 men on degarelix, under 1%, and 4 of 201 on leuprorelin, 2%. The median lengthening over the year was 12.0 milliseconds on degarelix and 16.7 on leuprorelin. A separate study in 80 healthy volunteers, given three to four times the blood level reached in treatment, found the drug itself has no effect on the heart's electrical recovery — the change comes from removing testosterone, not from the molecule.; Monthly electrocardiograms through 12 months in the randomised trial, plus a dedicated cardiac study in 80 healthy subjects.; Measured in people; Source [01]Source [02]
The immune system's reaction to the drug itself: Because degarelix is a short protein chain, the body can learn to make antibodies against it. Antibodies were found in 10% of men after a year of treatment and in 29% of men treated for up to five and a half years. Over that period there was no sign that the drug worked less well or caused more trouble in the men who had them.; Measured in the men who continued the original trial into its long extension, up to 5.5 years of treatment.; Measured in people; Source [01]Source [02]
Blood counts: Red cell counts fall. Among men who started with normal values, 40% dropped to a haematocrit of 0.37 or below and 13 to 15% to a haemoglobin of 115 grams per litre or below. Haemoglobin is the protein that carries oxygen and haematocrit is the share of blood made up of red cells. This happened to the same degree on degarelix and on leuprorelin, and the product information says openly that nobody knows how much of it is the cancer and how much is the treatment.; Laboratory values tracked through 12 months in both arms of the randomised trial.; Measured in people; Source [01]
Bones: Testosterone is what keeps bone being rebuilt, so any drug that removes it is expected to thin bone. Thinning bone and osteoporosis appear in the pooled list of reactions to degarelix, in the uncommon band of between 1 in 1,000 and 1 in 100. But the underlying measurement was never made: the EU product information states in plain words that bone density has not been measured during treatment with degarelix, and points instead to what has been published about men who had their testicles removed or were treated with the older agonist drugs.; Not measured. The expectation is carried across from surgical castration and from the agonist drugs, and is stated as such in the product information.; Claimed, never tested; Source [01]Source [02]
Blood sugar: New or worsening diabetes is a known consequence of blocking testosterone, and high blood sugar and diabetes appear on the degarelix reaction list in the uncommon band. The product information tells doctors that men with diabetes may need their blood sugar checked more often. It then says what has not been done: the effect of degarelix on insulin and glucose levels has not been studied.; Not measured. What is on the label is a class expectation drawn from men who had their testicles removed or took the older agonist drugs, plus spontaneous reports.; Claimed, never tested; Source [01]

What changed when it was measured

11 findings · 9 measured in people, 2 where studies in people disagree

In the 12-month randomised trial behind both approvals (620 men randomised, 610 treated), 97.2% of the 207 men on the approved degarelix dose held testosterone at castration level from day 28 to day 364, against 96.4% of the 201 men on monthly leuprorelin 7.5 mg — equal, not better. The difference is speed: 96% of the degarelix group were at castration level by day 3 against 0% on leuprorelin, and not one had the initial testosterone surge that most leuprorelin patients had. The widely repeated claim that this makes degarelix safer for the heart came from a re-analysis of six earlier trials done after the fact (2,328 men; the hazard ratio of 0.44 is from the subgroup who already had heart disease), which its own authors called hypothesis-generating. PRONOUNCE was built to test it and could not: it stopped early at 545 of 900 planned participants, and serious heart events occurred in 5.5% (15 of 275) on degarelix against 4.1% (11 of 269) on leuprolide, hazard ratio 1.28 with a range from 0.59 to 2.79. Pooling eight studies in 138,065 patients, with the databases searched to the end of 2023, also finds no difference. No trial has compared degarelix with an agonist for survival, and the EU product information states that bone density has never been measured during degarelix treatment.

Day 1: half the men are already at the castration level of 0.5 ng/ml. Day 3: 96% are, against nobody on monthly leuprorelin, and testosterone is down an average of 94% instead of up 65%. The injection site is at its worst here too — the pain typically comes on some hours after the injection, not during it. Day 7 to day 28: 99% then 100% at the castration level, and the redness and lump from the first double injection settle over a few days. Two weeks: PSA down 64%. One month: PSA down 85%, and the first maintenance injection is due; from here injection site reactions become much less frequent. Three months: PSA down 95%. Six to twelve months: hot flushes, tiredness, shrinking testicles and loss of erections are established, and testosterone stays down in about 97 men in every 100. After stopping, the depot empties slowly — the drug's own half-life on the monthly dose is about 29 days — and testosterone took a median of 112 days to climb back above the castration level and 168 days to reach the bottom of the normal range.

Keeping testosterone at the castration level for a year: 97.2% of the men on degarelix stayed below 0.5 ng/ml from day 28 to day 364, with a likely range of 93.5% to 98.8%, against 96.4% on monthly leuprorelin, likely range 92.5% to 98.2%. That is equal performance, not better performance.; 207 men on degarelix 240/80 mg and 201 on leuprorelin 7.5 mg, out of 620 randomised and 610 treated, 12 months, open label; Measured in people; Source [01]Source [11]
How fast testosterone reaches the castration level: On day 3, 96% of the degarelix group were at or below 0.5 ng/ml against 0% of the leuprorelin group. On day 7 it was 99% against 1%, and on day 14, 100% against 18%. By day 28 both arms were at 100%.; The same 207 men against 201, measured on days 1, 3, 7, 14 and 28; Measured in people; Source [01]
The initial testosterone surge: None of the men on degarelix had a surge, defined as testosterone going 15% or more above their starting level within two weeks. Most of the men on leuprorelin did. At day 3, testosterone was down an average of 94% on degarelix and up an average of 65% on leuprorelin.; The same randomised trial, first two weeks; Measured in people; Source [01]Source [05]
Serious heart events in men who already had heart disease — the trial built to answer it: Death, heart attack or stroke happened to 15 of 275 men on degarelix, 5.5%, and 11 of 269 on leuprolide, 4.1%. The hazard ratio was 1.28, pointing slightly against degarelix, and the range the true figure most likely sits in runs from 0.59 to 2.79 — wide enough to hold a large benefit and a large harm at once. The difference was not statistically significant, at p equal to 0.53.; 545 men with prostate cancer and existing narrowed-artery disease, randomised at 113 sites in 12 countries, 12 months. The trial was designed for 900 and stopped early because both recruitment and the number of heart events came in below what was planned.; Measured in people; Source [03]Source [04]
Death from a heart cause, heart attack or stroke in the same trial: 3.3% of the men on degarelix against 2.6% on leuprolide, hazard ratio 1.20 with a likely range of 0.45 to 3.23, not statistically significant at p equal to 0.71.; The same 545 men, to day 336; Measured in people; Source [03]
Reactions where the needle went in: 35% of the men on degarelix against under 1% on the injection into muscle. Pooling five randomised trials the gap is wider still: 49% against 0.6%, an odds ratio of 10.62 with a likely range of 2.94 to 38.31.; 207 men against 201 in the approval trial; 1,719 men in five randomised trials, 1,061 on degarelix and 658 on agonist drugs; Measured in people; Source [02]Source [12]
Hot flushes: 26% of the men on degarelix against 21% on leuprolide in the approval trial. Pooled across five randomised trials the figures were 29% against 27%, an odds ratio of 1.06, which is no difference.; 207 men against 201 over 12 months; then 1,719 men across five randomised trials; Measured in people; Source [02]Source [12]
Weight: Weight gain was recorded in 9% of the men on degarelix against 12% on leuprolide. The EU product information puts weight increase at 7% over a year of degarelix.; 207 men against 201 over 12 months; Measured in people; Source [01]Source [02]
Getting testosterone back after stopping: Median 112 days to rise back above the castration level, counted from four weeks after the last injection, and 168 days to get back above the bottom of the normal range. Everyone in that study had degarelix, so there is no comparison group and no figure for the older drugs beside it.; Men with a rising PSA after surgery or radiotherapy, given degarelix for seven months and then watched for seven months; Measured in people; Source [01]
Where the heart claim came from in the first place: Pooling six earlier randomised trials after the fact, cardiac events in the first year happened at about 44% of the agonist rate in men who already had heart disease, hazard ratio 0.44 with a likely range of 0.26 to 0.74. The authors wrote that because the analysis was done after the fact, their findings should only be read as generating a hypothesis. The trial run to test that hypothesis, above, did not confirm it.; 2,328 men enrolled in six phase 3 randomised trials between 2005 and 2012; Studies in people disagree; Source [07]
Serious heart events, pooling everything published up to the end of 2023: Across eight studies, serious heart events came at 0.94 times the agonist rate, a likely range of 0.65 to 1.35, which is no difference. Stroke, heart attack, death from any cause and abnormal heart rhythm were all no different either. Heart failure alone came out lower, at 0.56 with a range of 0.36 to 0.88 — on two of the eight studies, both of them look-backs through records.; 138,065 patients in eight studies — one randomised trial and seven that looked back through medical records; Studies in people disagree; Source [08]

What can go wrong

11 effects, 4 serious

A red, swollen, painful lump where the needle went in is the signature problem: 35% of men against under 1% on the older injection into muscle, and 49% against 0.6% pooled across five randomised trials. Hot flushes (26% vs 21%) and raised liver enzymes on a blood test (10% vs 5%) follow. Shrunken testicles, loss of erections, breast growth, tiredness and falling red cell counts come from having no testosterone and last as long as treatment does. Severe allergic reactions including anaphylaxis, and rarely an infected or broken-down injection site, are reported after marketing. Removing testosterone lengthens the heart's electrical recovery time, though the molecule itself has no such effect. Bone density and blood sugar were never measured in the degarelix trials.

A severe allergic reactionSerious: Anaphylaxis, hives and swelling under the skin have been reported. The US label says to stop the injection if a severe reaction occurs, and both labels make a previous severe reaction to degarelix or to anything else in the vial an outright bar to ever giving it again. Men with a history of severe untreated asthma, of anaphylaxis, or of severe hives or swelling were never included in the studies.; Rare on the EU list, meaning fewer than 1 in 10,000 for anaphylaxis, with less severe hypersensitivity in the uncommon band of between 1 in 1,000 and 1 in 100. These came from reports after the medicine was already on the market.; Source [01]Source [02]
An injection site that becomes infected or breaks downSerious: Most reactions at the injection site are a red painful lump that settles in a few days. Very occasionally the site becomes infected, forms an abscess or the tissue dies, and surgery or drainage is needed. Fewer than 1 in 100 men stopped treatment because of injection site problems of any kind.; Very rare in the EU product information. In the long extension study, 1% of 385 men had an injection site infection, including abscesses.; Source [01]Source [02]
Heart attack, heart failure and abnormal heart rhythmSerious: Blocking testosterone in any way has been linked to strokes and heart attacks, and both labels tell doctors to weigh a man's existing heart risk before starting. Degarelix itself does not appear to disturb the heart's electrical rhythm — the volunteer study found no effect at three to four times the treatment blood level — but taking testosterone away does lengthen the recovery interval.; Heart attack and heart failure are listed as rare, fewer than 1 in 1,000. Abnormal rhythm, palpitations and a lengthened QT interval are uncommon, between 1 in 1,000 and 1 in 100. In the one trial that measured heart events on purpose, in men who already had heart disease, they happened to 5.5% on degarelix and 4.1% on leuprolide over a year.; Source [01]Source [03]
Muscle breakdown and a fever with a collapsed white cell countSerious: Rhabdomyolysis is the breakdown of muscle tissue, which can damage the kidneys. Neutropenic fever is a fever when the white cells that fight infection have dropped, and is treated as an emergency. Both are single entries on the rare line of the label rather than events with published trial figures.; Both listed as rare, fewer than 1 in 1,000, in the pooled safety table covering 1,259 patients and 1,781 patient-years.; Source [01]
A red, swollen, painful lump where the injection went in: It comes almost entirely with the large starting dose, which is given as two injections, one on each side of the abdomen. During monthly maintenance the rate falls to about 3 episodes of pain per 100 injections. Reactions are usually mild to moderate and pass in a few days, and severe ones occurred in 2% of men or fewer. The product information tells staff not to inject where a waistband or belt will press on the site.; The most common effect by far: 35% of men on degarelix against under 1% on the injection into muscle. Pain 28%, redness 17%, swelling 6%, hardening 4%, lump 3%.; Source [01]Source [02]
Hot flushes and sweats: A sudden feeling of heat in the face, neck or chest, often with sweating, and often worse at night. It is a consequence of having no testosterone rather than of this particular drug, which is why the figures are almost the same on both treatments.; 26% of the men on degarelix against 21% on leuprolide over a year; the EU product information puts it at 25% and classes it as very common, meaning more than 1 in 10.; Source [01]Source [02]
Chills, fever and feeling fluish for a day after the injection: It starts within hours of the injection rather than days later, and passes. It is listed on the EU label alongside the injection site reactions, in the same group of things the depot does as it settles.; Transient chills in 3%, fever in 2% and flu-like illness in 1% of the men in the approval trial. Chills were recorded in 5% of the degarelix group against 0% of the leuprolide group.; Source [01]Source [02]
Raised liver enzymes: This is a blood test result rather than something a person feels. The rises are mild, generally reversible and are not accompanied by a rise in bilirubin or by symptoms. Men with known liver problems were excluded from the trials, and the product information advises checking liver function in them.; 10% of the men on degarelix against 5% on leuprolide in the approval trial. Over a median of about 43 months on the drug, mild or moderate rises were recorded in 47% of 385 men and severe ones in 1%, with no comparison group.; Source [01]Source [02]
Tiredness and weakness: The EU product information warns that tiredness and dizziness may affect the ability to drive or use machines. Reports to a side-effect database say nothing about how often something happens, because there is no count of how many men took the drug.; Listed as common on the EU label, meaning between 1 in 100 and 1 in 10. In the US trial table it sits in the 1% to under 5% band. It is the single most reported problem in the US public database of suspected side effects for this drug, with 405 reports of tiredness and 222 of weakness.; Source [01]Source [13]
Shrunken testicles, erection problems and breast growth: These follow from having no testosterone and continue for as long as treatment does. Reduced sex drive is listed separately, in the uncommon band, which sits oddly beside how often men describe it; the labels record what was written down in a trial, not what men say afterwards.; All three are common on the EU label, meaning more than 1 in 100 men and fewer than 1 in 10, and each was reported in at least 1% of men in the US trials.; Source [01]Source [02]
Falling red blood cell counts: Anaemia means too few red cells to carry oxygen well, and it shows up as tiredness and breathlessness. The product information states that it is unknown how much of this comes from the prostate cancer itself and how much from removing testosterone.; Among men who started with normal values, 40% fell to a haematocrit of 0.37 or below and 13 to 15% to a haemoglobin of 115 g/l or below — the same on degarelix as on leuprorelin.; Source [01]

Who it is known to be dangerous for

Anyone who has had a severe allergic reaction to degarelix or to mannitol, the sugar alcohol the powder is made up with — that is the only outright contraindication on both labels. Women: degarelix has no indication in women, and in pregnant animals it caused loss of pregnancy and death of the developing young at doses below the human starting dose. Children and teenagers: there is no relevant use, and the European regulator waived paediatric studies altogether. Men with severe liver or severe kidney impairment were never studied and the labels say to be cautious. Men born with a long QT interval, with heart failure, with unstable salt levels in the blood, or already taking medicines that lengthen the heart's electrical recovery need the balance weighed first. And men with a history of severe untreated asthma, of anaphylaxis, or of severe hives or swelling under the skin were excluded from the studies, so nothing is known about them. The medicine goes under the skin of the abdomen only: never into a vein, and injection into muscle has not been studied.

The amounts the studies used

5 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.

NCT00295750, the 12-month randomised trial behind both the EU and US approvals, in men with prostate cancer needing hormone-blocking treatment: 240 mg to start, given as two injections of 120 mg under the skin of the abdomen, then 80 mg under the skin once a month; 12 months, in 620 men randomised and 610 treated across three arms; Source [01]Source [11]
The third arm of that same trial, which was studied and then not approved — a useful reminder that a dose being tested is not a dose being endorsed: 240 mg to start, then 160 mg under the skin once a month; 12 months. The US label states plainly that FIRMAGON is not approved for use with monthly doses of 160 mg.; Source [02]
NCT00451958, the long extension in which men who finished the original trial carried on, plus men who crossed over from leuprolide: 80 mg under the skin every 28 days; A median of about 43 months, range 1 to 58 months, in 385 patients with no comparison group; Source [02]Source [14]
NCT02663908 (PRONOUNCE), the trial that set out to compare heart safety in men who already had narrowed arteries: 240 mg to start then 80 mg monthly under the skin, against leuprolide 22.5 mg into muscle every three months; 12 months, in 545 men, against the 900 the trial was designed for; Source [03]
The randomised trial of hormone treatment given before radiotherapy in high-risk localised or locally advanced prostate cancer: 240 mg to start then 80 mg monthly under the skin; Three months, in 244 men; 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.

The lump in the belly is what men actually talk about

The busiest degarelix thread on the largest English-language advanced prostate cancer board was started by a man two injections in, who describes an oval of redness four to six inches across, swelling about the size of a baseball and a hard lump about the size of a golf ball. He writes that there is no pain during the injection, that it sets in about four hours later and lasts a day, that most of it is gone by day three and that by day five or six nothing is left but a marble-sized lump. It drew 48 replies. He also says he can live with it as long as his PSA stays undetectable, which is roughly where the thread lands.

Read in Advanced Prostate Cancer community on HealthUnlocked, thread FIRMAGON INJECTION REACTIONS, 48 replies

What the published studies say

The trial tables record 35% of men having a reaction against under 1% on the injection into muscle, and describe them as mostly transient and mild to moderate, with under 1% of men stopping because of them. They do not record how big the lump was, which is the thing every man in the thread wants to know.

Men blame the nurse's technique; the trials suggest it is the drug

A thread opened on a second board in October 2015, and answered over the next two days, is entirely about injection technique — depth, the 45-degree angle, how long the vial is swirled, how slowly the plunger is pushed, whether the needle is left in afterwards, icing the site. The man who started it says he has had a reaction every single time and that the technique he is given varies with every nurse. He quotes a urologist saying about 30% of people get a reaction and that it is probably technique-related. Several repliers say technique fixed it for them.

Read in ZERO Prostate Cancer Support Community on Inspire, thread Firmagon injection technique and site reactions, opened October 2015, 9 replies

What the published studies say

Pooling five randomised trials, injection site reactions occurred in 49% of men on degarelix and 0.6% of men on the agonist injections — an odds ratio of 10.62. Technique may change how bad it is; the gap between 49% and 0.6% is the depot, not the nurse.

A day or two of feeling fluish after each shot, which nobody warned them about

In the same HealthUnlocked thread, a man a year into treatment reports injection site swelling together with a body temperature about 2°C above normal for two days after each injection, measured with a fitness tracker rather than a thermometer. Others in the thread describe similar short-lived whole-body reactions and note how little is written about what the depot does over years of monthly injections into the same area.

Read in Advanced Prostate Cancer community on HealthUnlocked, thread FIRMAGON INJECTION REACTIONS

What the published studies say

The EU product information records transient chills in 3%, fever in 2% and flu-like illness in 1% of patients, starting hours after dosing. Nothing published follows what repeated monthly depots do to the same patch of abdominal fat over years.

Whether to switch to something less awkward

The thread turns quickly into a discussion about switching. Men weigh a monthly clinic visit and a sore belly against a three-monthly injection of the older drugs, or against a daily tablet that works on the same receptor, which two posters name. The man a year into treatment writes that convenience is all his doctors want to talk about, and that he is staying on degarelix anyway because he does not want the agonist's first-week testosterone flare.

Read in Advanced Prostate Cancer community on HealthUnlocked, thread FIRMAGON INJECTION REACTIONS

What the published studies say

The EU product information is blunt about the one thing this choice usually turns on: the clinical benefit of degarelix compared with leuprorelin plus an anti-androgen tablet in the initial phase of treatment has not been demonstrated.

Where to read it yourself

Advanced Prostate Cancer community on HealthUnlocked
Forum
An online support group of 26,672 members and 31,533 posts, run by Malecare, an American prostate cancer support charity, with named administrators and a posted code of conduct.
Almost everyone posting is a man with advanced prostate cancer or his partner, and the community skews to men whose disease is serious enough to need this class of drug. Nothing posted is checked for accuracy. The charity asks for donations on the same pages. Men whose treatment is going quietly rarely start a thread, so the board over-represents trouble.
ZERO Prostate Cancer Support Community on Inspire
Forum
A prostate cancer discussion board hosted on Inspire, a commercial patient-network platform, in partnership with the American charity ZERO Prostate Cancer.
Inspire is a company that also sells patient-recruitment and research services to the pharmaceutical industry, and the pages carry advertising. Much of the degarelix material is a decade old, from when the drug was new. Most content is behind a sign-up wall, so what a visitor sees is a sample chosen by the site.
openFDA adverse event reports for degarelix
Official side-effect reports
The US regulator's public file of suspected side effects, queryable by drug. As read for this record it held 5,247 reports naming degarelix, most often tiredness, injection site pain, hot flushes and redness at the injection site.
A report only means somebody suspected a link, not that the drug caused anything, and the regulator says so. There is no count of how many people took the drug, so no rate can be worked out. Manufacturers file most reports, and serious events are far more likely to be reported than mild ones.
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. Not every substance has a profile, and the site invites you to ask if the one you want is missing.
Same limits as any spontaneous reporting scheme: a report is a suspicion, there is no denominator, and there is roughly a month's delay before a report appears. Reports come from healthcare professionals, the public and manufacturers alike.

What nobody has measured

13 unknowns

Whether degarelix is kinder to the heart than the agonist drugs. The trial built to answer that question stopped at 545 of the 900 men it needed, reported 5.5% against 4.1% the wrong way round, and left a range running from 0.59 to 2.79 — room for a large benefit and a large harm at the same time.
Whether men live longer on it. No trial has compared degarelix with an agonist for survival; the approval rests entirely on testosterone levels and PSA, and the US label states that no evidence links how fast PSA falls to any clinical benefit.
What it does to bone. The EU product information says bone density has not been measured during treatment with degarelix, and nothing published since fills that in.
What it does to blood sugar and insulin. The same document says that has not been studied either, while listing new and worsening diabetes as an uncommon reaction.
Whether avoiding the first-week hormone flare actually helps anyone. The EU product information states that the clinical benefit of degarelix compared with leuprorelin plus an anti-androgen tablet in the initial phase has not been demonstrated.
How it compares with relugolix, the daily tablet that blocks the same receptor. No published trial has put the two against each other; relugolix was tested against leuprolide.
Why about a third of men get a painful lump at the injection site and others get none. Volume, depth, injection speed and the depot itself have all been argued for; no trial has randomised the technique.
What happens to the same patch of abdominal fat after several years of monthly depots. Men on the boards raise scarring and whether a scarred site releases the drug properly; nothing published addresses it.
What antibodies against the drug do in the long run. They were present in 29% of men treated for up to five and a half years, and the product information says only that no effect on how well it worked or how safe it was had been seen by then.
Whether the lower rate of heart failure in the 2025 pooled analysis is real. It rests on two of the eight studies, both of which looked back through records rather than randomising anyone, and the same analysis found no difference in heart attack, stroke, rhythm problems or death.
How safe it is in severe liver or severe kidney impairment. Those men were excluded from every trial.
How long men can safely stay on it. The longest published follow-up is a median of about 43 months in an extension of the original trial, with everyone on the drug and nobody to compare against.
What it does in women or in anyone under 18. There is no indication in either group, the European regulator waived paediatric studies entirely, and in pregnant animals it killed the developing young at doses below the human starting dose.

Questions people ask

9 questions

What is degarelix used for?: It treats prostate cancer that feeds on testosterone — advanced disease, and higher-risk disease that is still confined or locally spread, where it is given before or alongside radiotherapy. It works by shutting testosterone down to the level a man would have after having his testicles removed. It is sold as Firmagon and given as an injection under the skin of the abdomen by a nurse or doctor.; Source [01]Source [02]
Does degarelix work?: For the job it is licensed to do, yes. In the trial behind its approval, 97.2% of the men on degarelix held testosterone at the castration level from day 28 through the whole year, against 96.4% of the men on monthly leuprorelin — the same, not better. What is different is the speed: 96% of the degarelix group were there by day 3 against nobody in the other group. No trial has shown that men live longer on degarelix than on the older injections.; Source [01]Source [12]
Degarelix vs Lupron — what is the actual difference?: Lupron and its relatives switch the hormone signal on hard before exhausting it, so testosterone spikes for the first week and then falls over three to four weeks; degarelix blocks the same switch directly, so there is no spike and testosterone is down within days. That means no anti-androgen tablet is needed as cover at the start. After the first month the two are equivalent on testosterone and PSA. The trade-offs are practical: degarelix is a monthly injection that leaves a sore lump in about a third of men, while the agonists can be given every three or six months and almost never do.; Source [01]Source [02]
Is degarelix better for the heart than the older injections?: Nobody knows, and this is the most important thing on this page. The idea came from a re-analysis of six old trials, done after the fact, which found about half as many cardiac events on degarelix in men who already had heart disease — its own authors called that hypothesis-generating. A trial called PRONOUNCE was then built to test it properly and could not finish: it stopped at 545 men of the 900 planned, and reported heart events in 5.5% of the degarelix group against 4.1% of the leuprolide group, a difference that could easily be chance. Pooling everything published up to the end of 2023 gives no difference either.; Source [04]Source [07]Source [08]
What are the side effects of degarelix?: The common ones are a red painful lump where the needle went in, in about a third of men; hot flushes in a quarter; and raised liver enzymes on a blood test in one in ten. Shrunken testicles, loss of erections, breast growth, tiredness and weight change follow from having no testosterone and continue for as long as treatment does. Rare but serious problems include severe allergic reactions, an infected or broken-down injection site, and heart rhythm trouble.; Source [01]Source [02]
Does degarelix weaken your bones?: Probably, but it was never measured. Thinning bone and osteoporosis appear on the reaction list in the uncommon band, and taking testosterone away is known to thin bone in men who have had their testicles removed or taken the older drugs. The EU product information states in one flat sentence that bone density has not been measured during treatment with degarelix, which after more than fifteen years on the market is a striking gap.; Source [01]Source [02]
How long does degarelix take to work?: Faster than anything else in its class. Half of the men in the trial were at the castration testosterone level within one day, 96% within three days and everyone within a month. PSA, the blood marker used to follow the cancer, was down 64% at two weeks, 85% at one month and 95% at three months. Coming off it is slow in the other direction: testosterone took a median of 112 days to climb back above the castration level.; Source [01]
Can you buy degarelix?: No. It is a prescription-only hospital medicine that arrives as a powder, has to be mixed with liquid immediately before use, and must be injected under the skin of the abdomen by a healthcare professional — never into a vein, and injection into muscle has never been studied. It is also not a compound anyone would want outside its licensed use: its entire effect is to remove testosterone, which is the opposite of what the peptides sold online are marketed for.; Source [01]Source [02]
Is degarelix banned in sport?: It does not appear on the 2026 World Anti-Doping Agency Prohibited List. The relevant section, S2.2.1, bans testosterone-stimulating peptides in men and names the hormone GnRH together with its agonist copies — goserelin, leuprorelin, triptorelin and others. Degarelix is the opposite kind of molecule, an antagonist that blocks the same receptor and lowers testosterone rather than raising it, and the word degarelix does not appear anywhere in the document.; Source [06]

Sources

14 sources

Cancer care · Hormones

18 peptides · strongest evidence first