Degarelix (Firmagon®)

Degarelix is a hormonal therapy drug used to treat prostate cancer. It’s best to read this information with our general information about prostate cancer.

You have degarelix as an injection just under the skin (subcutaneously). Your cancer doctor or nurse will tell you how often you will have it.

Like all hormonal therapy drugs, degarelix can cause side effects. Some of these can be serious so it’s important to read the detailed information below. How hormonal therapy affects people varies from person to person. Your doctor or nurse can talk to you more about this and give you advice on how to manage any side effects.

Tell your doctor or nurse straight away if you feel unwell or have severe side effects, including any we don’t mention here. If you need to see a health professional for any reason other than cancer, always tell them that you are having this treatment.

How degarelix works

Hormones are substances produced naturally in the body. They act as chemical messengers and help control the activity of cells and organs. Hormonal therapies interfere with the way hormones are made or how they work in the body.

Most prostate cancers need the hormone testosterone to grow. Almost all testosterone in men is made by the testicles. A very small amount is made by the adrenal glands, which sit above the kidneys. Degarelix stops the testicles from making testosterone. This reduces testosterone levels and may shrink the prostate cancer or stop it growing.

When degarelix is given

Degarelix is used to control prostate cancer in men whose cancer has spread to other parts of the body (advanced or metastatic prostate cancer).

Some men may have intermittent therapy with degarelix. This involves having degarelix treatment for a few months until the cancer is at a very low level. This is measured by a blood test called the PSA test. You then have a break from treatment and restart degarelix when needed.

Your doctor or nurse will explain how long you will have degarelix for.

How degarelix is given

Degarelix is given as an injection just under the skin (subcutaneously) of the tummy. On the first day of treatment, a nurse will give you two injections of the drug. After this, you’ll have one injection a month.

The injections will usually be given by your practice nurse at your doctor’s surgery. If you’re not able to visit the surgery, a district nurse can give you the injection at home. If an injection is delayed by two to three days this should not affect how well the treatment works. But you should try to have your injections as regularly as possible.

Some people may find the injection slightly uncomfortable and notice redness or a darker colour around the area afterwards. Let your doctor know if this starts to worry you.

Possible side effects of degarelix

We explain the most common side effects of degarelix here. We also include some rarer side effects. You may get some of the side effects we mention, but you are very unlikely to get all of them. If you are having other drugs as well, you may have some side effects that we don’t list here.

You will see a doctor or nurse regularly while you have this treatment. Always tell your doctor or nurse about the side effects you have. They can prescribe drugs to help control them and give you advice about managing them. Don’t stop taking degarelix without talking to your doctor first.

More information about this drug

We’re not able to list every side effect for this treatment here, particularly the rarer ones. For more detailed information you can visit the electronic Medicines Compendium (eMC).

Allergic reaction

Sometimes, degarelix may cause an allergic reaction within a few hours of being given. Signs of a reaction can include:

  • raised itchy rash
  • feeling flushed, dizzy or short of breath
  • having pain in your back, tummy or chest
  • feeling generally unwell.

If you develop any of these symptoms, contact your doctor straight away for advice.

Chills, fever or flu-like symptoms after the injection

Some men develop these symptoms a few hours after having the injection. They usually settle within a few hours. Contact your cancer nurse or doctor if you have them. They can advise you on what to do.

Hot flushes and sweats

These are common and can be mild or more severe. During a flush you feel warmth in your neck and face and your skin may redden. Mild flushes last for a few seconds up to about a couple of minutes. More severe flushes can last for 10 minutes or more. You may have sweats then feel cold and clammy. Some people feel anxious or irritable during a hot flush.

There are things you can do to try to reduce flushes, such as cutting down on nicotine, alcohol and hot drinks that contain caffeine such as tea and coffee.

If hot flushes are troublesome, your doctor can prescribe drugs to help reduce them.

Hot flushes and sweats may lessen as your body adjusts to hormonal treatment. They usually stop completely a few months after treatment finishes.

Sexual effects

Most men lose their sex drive and have erection difficulties during hormonal therapy. These often return to normal after you stop taking the drug, but some men continue to have difficulties after treatment is over. Your doctor can prescribe treatments to help with erection difficulties but these don’t affect sex drive.

If you need support coping with sexual difficulties, your nurse or doctor can give you information and refer you for specialist support services.


You may feel tired and lack energy. Try to pace yourself if you feel tired. Aim for a balance between resting and being physically active. Regular exercise can reduce tiredness in men having hormonal therapy. Ask your doctor or nurse what is safe for you to do.

If tiredness makes you feel sleepy, don’t drive or operate machinery.

Skin rashes

Occasionally, people develop a mild skin rash. This often gets better without treatment. Tell your doctor if you have a rash.

Muscle or bone pain

If you have soreness or stiffness in your muscles or bones, your doctor can prescribe painkillers to ease this.

Feeling sick

This is usually mild. Your doctor can prescribe anti-sickness drugs if needed.


Drink plenty if you have diarrhoea. Try to drink at least two litres (about three and a half pints) of fluids each day. Your doctor can prescribe anti-diarrhoeal tablets if needed.

Dizziness, blurred vision or drowsiness

Occasionally, degarelix can cause these side effects. Don’t drive or operate machinery if you have them. Talk to your doctor if you are worried about this.

Possible side effects of long-term degarelix treatment

Weight gain and loss of muscle strength

You may gain weight, particularly around your waist, and you may lose some muscle strength. Eating a healthy diet and exercising regularly can help control your weight. Resistance exercises, such as lifting weights, may help you to reduce loss of muscle strength. Ask your doctor or nurse for advice.

Mood changes

You may experience mood swings. Some men can become low in mood or depressed after taking degarelix for several months or more. Tell your doctor if you notice any mood changes.

Memory and concentration

You may notice changes to your memory or ability to concentrate. Try using a notebook, post-it notes and a calendar to keep track of things. If you’re having problems, talk to your doctor.

Breast swelling or tenderness

You may notice slight breast swelling and tenderness. This is called gynaecomastia. Your doctor can advise you on how this can be prevented or treated.

Bone thinning (osteoporosis)

Taking degarelix for a few years increases your risk of bone thinning (osteoporosis), which can increase your risk of a broken bone (fracture).Your doctor can give you advice on how this can be monitored and treated. Regular walking and resistance exercises such as lifting weights can help to keep your bones strong. Eating a healthy diet, not smoking and staying within the recommended limits for alcohol will also help to protect your bones.

Let your doctor know if you have any discomfort in your bones or joints. We have more information on bone health that we can send you.

Anaemia (low number of red blood cells)

Degarelix can reduce the number of red blood cells in your blood. These cells carry oxygen around the body. If the number of red blood cells is low, you may be tired and breathless. Tell your doctor or nurse if you feel like this.

Effects on the liver

Degarelix can sometimes affect the liver. Usually, any effect is mild and you can continue to take degarelix. Your doctor may do regular blood tests to check your liver.

Risk of heart changes and diabetes

There may be an increased risk of developing heart disease, changes in heart rhythm or diabetes when taking degarelix. But the benefits of hormonal treatment generally outweigh the possible risks. You can talk to your specialist about the possible risks and benefits in your situation. It’s important to tell your doctors if you have ever had heart rhythm problems or if you’re taking any medicines for this.

You can help reduce your risk of heart disease and diabetes by:

  • not smoking
  • eating a healthy diet
  • staying within the recommended limits for alcohol
  • keeping to a healthy weight
  • being physically active.

Always let your doctor or nurse know about any side effects you have. There are usually ways in which they can be controlled or improved.

Other information about degarelix

Other medicines

Degarelix can affect how some other medicines work. If you’re taking medicines that are used to treat heart rhythm problems (such as procainamide, amiodarone and sotalol) or medicines that can affect heart rhythm (such as methadone, moxifloxacin and antipsychotics), let your doctor know before beginning treatment.

Tell your doctor about any medicines you are taking, including ones you can buy for yourself, complementary therapies, vitamins and herbal drugs.


Degarelix can affect your fertility (being able to father a child). If you are worried about this, you can talk to your doctor before treatment starts.

Medical treatment

If you need to go into hospital for any reason other than cancer, always tell the doctors and nurses that you are taking degarelix. Explain that you are taking hormonal therapy and that no one should stop or restart your treatment without advice from your cancer doctor. Give them the name of your cancer doctor so they can ask for advice.