Peptide Graded

All peptides / Reproduction

Degarelix

GnRH antagonist

Also Firmagon, FE200486, Degarelix acetate

Evidence
AStrong human evidence
FDA status
FDA approvedas of 2026-10-27
Route
Injection
Studies cited
1 human0 animal or cell

A shot that lowers testosterone to treat advanced prostate cancer. A trial of 610 men showed it works as well as an older drug, and faster.

Sold for

Degarelix has no wellness following; in oncology its selling point is speed, since it switches off testosterone in days without the initial flare that older hormone shots produce.

Studies say

A 610-man randomized trial showed degarelix matches leuprolide at suppressing testosterone over a year and gets there faster, which with approval supports an A.

Why grade A. Approval rested on the CS21 trial, a 12-month randomized open-label phase 3 study of 610 men with prostate cancer, which showed degarelix kept testosterone at castrate levels in over 97% of men, non-inferior to leuprolide, and did so within three days without the testosterone surge that agonists cause. 12

FDA. Degarelix is FDA-approved as Firmagon (degarelix for injection), approved in December 2008 for the treatment of advanced prostate cancer. 2

Written from 3 cited sources. Fact-checked 2026-10-27: 13 claims checked, 0 corrected. Last refreshed 2026-10-27. Not physician reviewed.

What this means for you

What people take it for
Advanced prostate cancer
Can a US doctor prescribe it?
Yes, FDA approved for advanced prostate cancer.
Properly tested in people?
Yes, in a large controlled trial of 610 men.

Evidence checklist

  • Randomised controlled trial CS21, randomized open-label phase 3yes
  • Human study over 100 people CS21 enrolled 610 menyes
  • More than one research group Registration trial from one programno information
  • Clinical outcomes, not surrogate markers Testosterone suppression, a surrogateno
  • Human safety data beyond case reports Trial and label adverse event datayes

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

What it is

Degarelix is a lab-made peptide with ten amino acids. It blocks the receptor for gonadotropin-releasing hormone (GnRH) in the pituitary. It belongs to the same antagonist class as cetrorelix and ganirelix, which are used in fertility treatment. Degarelix is made as a depot. It forms a gel under the skin and releases the drug for a month. Ferring Pharmaceuticals sells it as Firmagon. 2

It is used for androgen deprivation therapy. This lowers testosterone to starve prostate cancers that depend on it. 2

How it works

Testosterone drives prostate cancer growth. The body makes testosterone in response to luteinizing hormone (LH) from the pituitary. LH in turn depends on GnRH from the hypothalamus. Degarelix sits in the GnRH receptor without switching it on. So LH falls within hours, and testosterone follows within days. GnRH agonists such as leuprolide reach the same end point differently. They overstimulate the receptor until it shuts down. That takes two to four weeks. It also causes a temporary testosterone surge, which can worsen symptoms in men with bone metastases. 12

What human research shows

Klotz and colleagues randomized 610 men with prostate cancer who needed hormone therapy. The men got one of two degarelix regimens or monthly leuprolide for 12 months. The main measure was testosterone at or below the castrate threshold at every monthly check from day 28 to day 364. This held in 97.2% and 98.3% of the two degarelix groups. It held in 96.4% of the leuprolide group. That met the non-inferiority goal. 1

By day 3, about 96% of degarelix patients had castrate-level testosterone. None of the leuprolide patients did. They instead had a brief surge of around 65% above baseline. Prostate-specific antigen (PSA) fell faster with degarelix at days 14 and 28. 1

StudyModelFinding
CS21 (Klotz 2008)Humans, n=610 men with prostate cancer, randomized open-label phase 3, 12 monthsTestosterone held at castrate level in 97.2% to 98.3% on degarelix versus 96.4% on leuprolide; castrate level by day 3 in 96% versus 0%. 1
Firmagon prescribing informationRegulatory summaryApproved for advanced prostate cancer; injection-site reactions and QT prolongation listed. 2

Safety

All androgen deprivation shares the same side effects. These are hot flushes, weight gain, fatigue, loss of libido and erectile dysfunction. Bone density falls. Over time, metabolic changes raise cardiovascular risk. In CS21 these effects were similar across arms. 12

Injection-site reactions are specific to degarelix. They were much more common than with the intramuscular leuprolide shot. Patients had pain, redness and swelling at the abdominal injection site, mostly after the first dose. The label lists raised liver enzymes and QT-interval prolongation on the ECG, as it does for agonists. Degarelix is not approved for women or children. 12

A 2026 analysis used the FDA's adverse event reporting system through 2024. It found a disproportionate number of interstitial lung disease reports for seven antiandrogen drugs, degarelix among them. Most reports came from Japan. The authors call the signal exploratory and say it needs validation. 3

Questions for your clinician

  • How does degarelix differ from a leuprolide injection for my situation?
  • How will my bone and heart health be monitored on hormone suppression?
  • What injection-site reactions should I expect?

Questions people ask

Is degarelix FDA-approved?

Yes. It is sold as Firmagon, approved in 2008 for advanced prostate cancer. 2

How is degarelix different from leuprolide?

Both lower testosterone to castrate levels. Degarelix blocks the GnRH receptor directly and works within three days. Leuprolide first overstimulates the receptor and causes a temporary testosterone surge. Suppression sets in after a few weeks. In the CS21 trial, the 12-month suppression rates were equivalent. 1

What is the testosterone flare?

With GnRH agonists, testosterone rises about 65% above baseline in the first days before it falls. In men with spinal metastases, that surge can briefly worsen pain or nerve compression. Degarelix does not cause it. 1

What unwanted effects should patients plan for?

The usual effects of lowering testosterone are hot flushes, weight gain, fatigue, sexual side effects and bone loss. Degarelix also causes injection-site pain and swelling, which are more common than with leuprolide. 12

Citations

  1. Klotz 2008, BJU Int: efficacy and safety of degarelix, 12-month comparative randomized phase III study (CS21) doi.org
  2. Firmagon (degarelix for injection) prescribing information, Ferring, revised 2020 ferringusa.com
  3. Li 2026, Int Urol Nephrol: interstitial lung disease with antiandrogen agents, FDA adverse event reporting system analysis pubmed.ncbi.nlm.nih.gov

Updates

  • 2026-10-27 added FAERS interstitial lung disease signal across antiandrogens including degarelix (PMID 42154420) to safety, flagged as exploratory.

Related