Degarelix (Firmagon)

Degarelix is a hormone therapy drug and is also known by its brand name Firmagon.

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

How degarelix works

Prostate cancer depends on testosterone to grow. Drugs that stop the testes making testosterone can slow or stop the growth of prostate cancer cells. 

Degarelix works by blocking gonadotrophin releasing hormone receptors in the pituitary gland in the brain. The pituitary gland then stops producing luteinising hormone. The luteinising hormone is then not available to trigger the testes to make testosterone. 

How you have degarelix

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

Tests during treatment

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.

Side effects

How often and how severe the side effects are can vary from person to person. They also depend on what other treatment you are having. For example, your side effects could be worse if you are also having other drugs or radiotherapy.

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 for men and women. 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 that can cause breathlessness, tiredness and looking pale
  • weight gain
  • difficulty sleeping or getting to sleep
  • headaches and dizziness
  • diarrhoea
  • feeling sick
  • an increase of liver enzymes in the blood
  • excessive sweating including night sweats
  • rash
  • general discomfort or pain
  • 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

Rare side effects

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

  • an allergic reaction
  • high blood sugar levels that might become diabetes
  • high levels of cholesterol in the blood
  • weight loss
  • loss of appetite
  • high or low levels of calcium in the blood
  • 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
  • being sick
  • tummy (abdominal) discomfort or pain
  • dry mouth
  • an increase of bilirubin and alkaline phosphate in the blood
  • skin changes such as hives, nodules, itching and redness
  • bone thinning (osteoporosis)
  • muscle problems such as weakness, pain and spasms
  • swollen, stiff joints
  • leaking urine, waking to pass urine at night and passing small amounts often
  • passing dark coloured urine
  • difficulty or pain passing urine
  • problems with how well your kidneys work
  • pain in the testicles, breasts and the area between your hips (pelvis)
  • itching, burning or irritation of your penis and scrotum
  • failure to ejaculate
  • 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 some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.


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

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.

More information about this treatment

For further information about this treatment go to the electronic Medicines Compendium (eMC) website.

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

Related links