Degarelix (Firmagon) | Cancer Research UK
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What degarelix is

Degarelix is a type of hormone therapy called a gonadatrophin releasing hormone blocker. Degarelix is pronounced deh-ga-rel-ix. It is also called 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 gonadatrophin releasing hormone receptors in the pituitary gland in the brain. The pituitary gland then stops producing luteinising hormone. Luteinising hormone triggers 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). The first time you have degarelix you have two injections. Then you have one injection once a month. You continue with the treatment for as long as it works.

You can watch a video about giving injections just under the skin.


Tests during treatment

You 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.


About side effects

We've listed the side effects associated with degarelix. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.

You may have a few side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment. Or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)

The side effects may be different if you are having degarelix with other medicines.

Tell your doctor or nurse straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 men have one or more of these effects.


Occasional side effects

Between 1 and 10 in every 100 people have one or more of these.

  • Tiredness and weakness (fatigue) during treatment
  • Low levels of red blood cells (anaemia), which can cause tiredness and breathlessness
  • Weight increase happens in 7 out of 100 men (7%)
  • Difficulty sleeping
  • Dizziness and headaches – don't drive or operate machinery if you feel dizzy or very tired
  • Diarrhoea – drink plenty of fluids. Tell your doctor or nurse if diarrhoea becomes severe or continues for more than 3 days
  • Feeling sick is usually well controlled with anti sickness medicines
  • Liver changes that are very mild and unlikely to cause symptoms – the liver will almost certainly go back to normal when treatment finishes
  • Flu like symptoms such as chills and fever for a few hours after the injection
  • A hard lump at the injection site
  • Increased sweating, especially at night
  • Skin rashes
  • Pain in your back, joints, muscles or bones
  • Breast tenderness and swelling – this can be distressing. Your doctor can prescribe medicines to help
  • Raised blood pressure
  • Shrinking of testicles

Rare side effects

Fewer than 1 in 100 people have these.

  • An allergic reaction to the drug – let your doctor or nurse know straight away if you feel breathless, or if you have swelling of your lips, face or throat
  • Changes in blood sugar levels – if you have diabetes you may need to check your blood sugar levels more often than usual
  • Raised cholesterol levels
  • Weight loss
  • Loss of appetite
  • Constipation – your doctor or nurse may give you laxatives to help prevent this. Tell them if you are constipated for more than 3 days
  • Swelling of the ankles and legs due to a build up of fluid (oedema), which is usually mild
  • Changes in your heart rhythm and blood pressure – your nurse or doctor will check your blood pressure and you will have regular ECGs
  • Skin changes, such as redness and itching
  • Bone thinning may occur with long term treatment
  • You may find that the levels of sugar in your blood change – you will have regular blood tests. If you have diabetes you will need to take extra care when checking your blood sugar
  • Sadness that may develop into depression
  • Being sick
  • Tummy (abdominal) pain
  • A dry mouth – drink plenty of fluids if you have this
  • Aches and pains in muscles or bones
  • Muscle weakness or spasms
  • Pain when passing urine or needing to go urgently – let your doctor or nurse know if you have this
  • Hair thinning
  • Higher levels of cholesterol in the blood
  • Leakage of urine (incontinence)
  • Blurred vision – don't drive if you have this

Important points to remember

Talk to your doctor, pharmacist or nurse about all your side effects so they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Other medicines

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.


This drug may harm a baby developing in the womb. It is important not to father a child while you are having treatment and for a few months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


More information on degarelix

This page doesn't list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at

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Updated: 3 July 2015