Degarelix

Degarelix (Firmagon) is a real, FDA-approved GnRH antagonist for advanced prostate cancer — mechanistically the mirror image of the GnRH agonists (leuprolide, goserelin, triptorelin) covered elsewhere on this site, because it suppresses testosterone immediately with no initial surge.

Antagonist, not agonist — why that matters

Degarelix is a synthetic linear decapeptide GnRH (LHRH) antagonist — mechanistically distinct from the GnRH agonists covered on this site's leuprolide and gonadorelin pages. Agonists initially *stimulate* the pituitary GnRH receptor, causing a transient testosterone surge ("flare") before the receptor downregulates and suppression sets in — which is why agonist regimens require a co-administered anti-androgen in patients at risk of flare-driven complications (spinal cord compression, urinary obstruction). Antagonists like degarelix instead directly block the receptor from the first dose, so LH, FSH and testosterone fall immediately with no surge at all.

The approval and pivotal trial

The FDA approved degarelix (as Firmagon) on 24 December 2008 for advanced prostate cancer, based on the CS21 trial (Klotz et al., BJU Int 2008, PMID 19035858): a 610-patient, 12-month, non-inferiority trial against leuprolide. More than 96% of patients across all degarelix and leuprolide arms achieved and sustained castrate testosterone levels (below 50 ng/dL) from day 28 through day 364 — a clean non-inferiority result, not a mixed one — and degarelix reached castrate testosterone and reduced PSA faster than leuprolide, consistent with skipping the agonist flare phase.

Safety

The standout safety signal is injection-site reactions, more frequent than typical for the intramuscular GnRH-agonist depots because degarelix is a larger-volume subcutaneous injection: pain in about 28% of patients, redness in 17%, swelling in 6%, and roughly 1% injection-site infections or abscesses. Class-wide androgen-deprivation effects also apply (hot flashes, weight change, liver enzyme elevation, fatigue). In October 2010 the FDA required a class-wide label update for GnRH agonists on increased diabetes and cardiovascular risk; whether that update applies to degarelix specifically (an antagonist, not an agonist) isn't something we could confirm either way — check the current Firmagon label directly if this matters to you. A separate dedicated study found no direct effect of degarelix itself on cardiac repolarization (QT interval) at supratherapeutic doses, suggesting any cardiovascular risk is a class effect of testosterone suppression generally rather than something specific to this drug.

Current status

Still marketed by Ferring Pharmaceuticals. No FDA-approved generic degarelix exists as of this review — be wary of any site claiming otherwise, since the FDA itself has warned that fraudulent online sellers have offered purported "generic" versions. No FDA warning letter naming degarelix as a grey-market "research peptide" was found; it has no bodybuilding or cosmetic appeal, since testosterone suppression is the opposite of what that market wants.