Firmagon (degarelix) is a hormone therapy used to treat advanced prostate cancer. It belongs to a class of medicines called GnRH antagonists. It works by rapidly lowering testosterone levels in the blood, which slows or stops the growth of prostate cancer cells that rely on testosterone to grow.

Unlike older hormone therapies (LHRH agonists), Firmagon lowers testosterone immediately without causing an initial testosterone surge (known as a flare), which can temporarily worsen symptoms in some patients.

Firmagon is given as an injection under the skin of the abdomen (belly area) by a healthcare professional. You will not inject this medicine yourself.

Treatment starts with two 120 mg injections given on the same day, followed by one 80 mg injection every 28 days (monthly).

Keep all monthly appointments. Consistency is important to maintain low testosterone levels and control the cancer.

Your injections are administered in a clinic and scheduled in advance. If you need to reschedule an appointment, contact your specialist as soon as possible.

Because Firmagon is given by healthcare professionals, overdose is unlikely. If you have concerns about the dose you received, speak to your doctor.

Storage is managed by the treating clinic. Firmagon powder is stored at room temperature (below 30°C) and reconstituted with water for injection before use.

• Keep out of reach of children
• Do not use after the expiry date on the packaging

Like all medicines, Firmagon can cause side effects.

Very common side effects (affecting more than 1 in 10 people):

• Injection site reactions: pain, redness, or swelling at the injection site (usually settles within a few days)
• Hot flushes
• Weight gain
• Fatigue

Common side effects:

• Decreased sex drive
• Erectile dysfunction
• Night sweats
• Bone thinning (osteoporosis) with long-term use: your doctor may recommend calcium and vitamin D
• Changes in liver blood tests

Serious side effects:

• QT prolongation (abnormal heart rhythm): tell your doctor if you have a history of heart problems or are on medicines that affect heart rhythm

Report any unexpected symptoms to your doctor, especially chest discomfort or palpitations.

Tell your doctor about all medicines you take, especially:

• Medicines that can prolong the QT interval (affect heart rhythm), such as certain antiarrhythmics, antipsychotics, or antibiotics. Combining these with Firmagon may increase the risk of a heart rhythm problem

Always provide your full medicine list before starting Firmagon.

Why is Firmagon preferred over older hormone therapies for some patients?

Older LHRH agonists (such as Zoladex or Eligard) can cause an initial surge in testosterone before levels fall. This flare can temporarily worsen bone pain or urinary symptoms in men with advanced disease. Firmagon works differently, blocking the testosterone signal immediately without any surge, which is particularly important if you have symptoms that could be aggravated by a flare.

Will I lose bone strength?

Long-term low testosterone increases the risk of osteoporosis. Your doctor will likely recommend calcium and vitamin D supplements and may order regular bone density scans. Weight-bearing exercise is also helpful in maintaining bone strength during treatment.

Ace provides accurate and independent information medically reviewed on prescription medications. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment.