Degarelix (Firmagon)

Degarelix is a type of hormone therapy. It is also known as Firmagon.

Degarelix is a treatment for hormone dependent prostate cancer. Hormone dependent means that the cancer cells need a hormone in order to grow. 

You pronounce degarelix as deg-a-rel-ix.

How does degarelix work?

Prostate cancer depends on testosterone Open a glossary item to grow. Hormone therapy blocks or lowers the amount of testosterone in the body.

Degarelix works by blocking messages from a part of the brain called the hypothalamus that tells the pituitary gland Open a glossary item to produce luteinising hormone. Luteinising hormone tells the testicles Open a glossary item to produce testosterone. So degarelix stops the testicles making testosterone.

This type of hormone therapy is called a gonadotrophin-releasing hormone antagonist or GnRH blocker.

How do you have degarelix?

You have degarelix as an injection just under the skin (subcutaneously) into the fatty tissue of your tummy (abdomen). 

The video below shows you how to give an injection just under your skin.

How often do you have degarelix?

When you start treatment, you have 2 injections on the same day. Then you have one injection a month. 

How long you continue having degarelix for will depend on your situation. Your healthcare team will let you know more about this. 


You might have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

What are the side effects of degarelix?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

When to contact your team

Your doctor, nurse, or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Hot flushes

We have some tips for coping with hot flushes and the possible treatments. Talk to your doctor if your hot flushes are hard to cope with. They might be able to prescribe you some medicines.

Inflammation around the injection site

Tell your nurse if you notice any signs of redness or irritation around the injection site.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • a drop in red blood cells Open a glossary item that can cause breathlessness, tiredness and looking pale
  • weight gain, rarely you may lose weight
  • difficulty sleeping or getting to sleep
  • headaches
  • feeling dizzy
  • diarrhoea
  • feeling sick, rarely you may be sick
  • an increase of liver enzymes Open a glossary item in the blood, you have regular blood tests to check this
  • excessive sweating including night sweats
  • rash
  • discomfort or pain in your muscles, bones, or joints
  • growth of breast tissue (gynaecomastia) - talk to your doctor if this becomes a problem
  • your testicles become smaller
  • you might have problems getting or maintaining an erection (erectile dysfunction) - talk to your doctor or nurse if this becomes a problem
  • high temperature
  • chills
  • tiredness (fatigue)
  • flu like symptoms such as high temperature, feeling achy, cough, sore throat, and headache

Rare side effects

These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:

  • an allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness - some allergic reactions can be life threatening, alert your nurse or doctor if notice any of these symptoms
  • high blood sugar levels that might become diabetes Open a glossary item
  • high levels of a fatty substance called cholesterol in the blood, you have regular blood tests to check this
  • loss of appetite
  • high or low levels of calcium in the blood, you have regular blood tests to check this
  • feeling very low and sad (depression)
  • a decrease in your sex drive
  • difficulty thinking
  • reduced sense of touch
  • blurred vision
  • changes to your heart beat (rhythm)
  • high or low blood pressure
  • difficulty breathing
  • constipation
  • tummy (abdominal) discomfort or pain
  • dry mouth
  • skin changes such as nodules, itching and redness
  • hair loss or thinning
  • weakened bones that are fragile and more likely to break (osteoporosis)
  • muscle problems such as weakness, pain and spasms
  • swollen, stiff joints
  • problems passing urine such as leaking (incontinence), waking to pass at night, urgency to go, passing small amounts often, difficulty or pain passing urine
  • problems with how well your kidneys work – you have regular blood tests to check this
  • pain in the testicles, breasts and the area between your hips (pelvis)
  • itching, burning or irritation of your penis and scrotum
  • unable to ejaculate Open a glossary item 
  • a general feeling of discomfort, illness or unease the cause of which is not easy to identify
  • swelling of your hands and feet

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do I need to know

Other medicines, foods and drink

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Loss of fertility

This treatment might stop you being able to father a child.

Talk to your doctor before starting treatment if you think you may want to have a baby in the future. You may be able to store sperm before starting treatment.

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

  • Electronic Medicines Compendium
    Accessed January 2023

  • Degarelix for treating advanced hormone-dependent prostate cancer
    National Institute for Health and Care Excellence (NICE), August 2016

  • Degarelix (Firmagon®)
    Scottish Medicines Consortium, December 2010

  • Prostate cancer: diagnosis and management
    National Institute for Health and Care Excellence (NICE), May 2019. Last updated December 2021

Last reviewed: 
23 Jan 2023
Next review due: 
23 Jan 2026

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