Degarelix (Firmagon): Uses, Mechanism, and Side Effects

Men facing an advanced prostate cancer diagnosis often want to understand how hormone-blocking treatments actually work before starting one. Degarelix, sold under the brand name Firmagon, is one option used to lower testosterone levels that can fuel tumor growth.

Key takeaways

• Degarelix is a GnRH receptor antagonist approved for advanced prostate cancer, sold as Firmagon.
• It works by directly blocking pituitary GnRH receptors, reducing gonadotropin release and lowering testosterone.
• The compound has been studied across 174 registered clinical trials.
• The label does not carry a boxed warning.
• Frequently reported adverse events involve fatigue, hot flush, and injection site reactions.

What Degarelix Is

Degarelix belongs to a class of drugs called GnRH receptor antagonists. Rather than stimulating the pituitary gland the way earlier hormone therapies did, it binds reversibly to GnRH receptors and blocks them outright. This action reduces the release of gonadotropins, which in turn lowers testosterone production.

What Degarelix Is Approved For

Firmagon is indicated for the treatment of patients with advanced prostate cancer. As a GnRH receptor antagonist, it fits within a category of therapies used to manage hormone-sensitive disease. No boxed warning is listed on the label for this product.

What the Evidence Shows

Degarelix has been evaluated in 174 registered clinical trials. One completed Phase 2/3 extension study assessed the long-term safety of degarelix one-month depot dosing in patients with prostate cancer. A separate completed registry study observed clinical outcomes in patients with high-risk metastatic, hormone-naive prostate cancer in Japan. The compound has also been explored outside oncology, including a completed Phase 2 study examining hormonal intervention in hospitalized COVID-19 patients.

Reported Side Effects

Adverse event reports submitted to FAERS for degarelix most commonly describe general and injection-related symptoms. Fatigue (412 reports) and asthenia (224) were frequently noted, alongside hot flush (329), a known effect of reduced testosterone. Injection site reactions were also common, including pain (367), erythema (293), and swelling (212). Death (227) and product storage error (209) reports also appear in the data. These figures reflect the number of reports submitted, not confirmed incidence or a causal link to the drug.