Triptorelin (Decapeptyl SR, Gonapeptyl Depot) | Cancer Research UK
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What triptorelin is

Triptorelin is a type of hormone therapy drug used to treat prostate cancer. It is also called Decapeptyl SR or Gonapeptyl Depot. Researchers are also looking into using triptorelin as a treatment for breast cancer.


How triptorelin works

Triptorelin is a type of hormone therapy drug called a gonadotropin releasing hormone blocker. It lowers the level of testosterone in men and oestrogen in women. It does this by stopping the release of luteinising hormone from the pituitary gland. In men, this stops the testicles producing the male sex hormone, testosterone. In women, it stops the ovaries from producing oestrogen.

Prostate cancer depends on testosterone, to grow. Hormone therapies that lower the level of testosterone can slow down the growth of cancer or shrink it.

Some breast cancers depend on oestrogen to grow. Lowering the level of oestrogen can slow or stop the growth of the cancer.


How you have triptorelin

You have triptorelin either

  • As an injection into a muscle (usually in your bottom)
  • As an injection just under the skin of your tummy

You may have the injections once a month, every 3 months, or every 6 months.


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 triptorelin below. You can use the links to find out more about each side effect. Where there is no link, please go to our cancer drug side effects section 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 triptorelin with other drugs.

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


Temporary side effects when treatment starts

Men having triptorelin for prostate cancer may have an increase in symptoms called tumour flare for the first few weeks of the treatment. Your doctor may give you another type of hormone drug to start with, to try to prevent this. The symptoms of tumour flare include

  • Increased pain or difficulty passing urine
  • Bone pain in 1 in 5 men (20%). 
  • Back pain 
  • Blood in the urine 
  • A pins and needles feeling in the legs

Tell your doctor or nurse if you have any of these effects.


Common side effects

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

  • Hot flushes and sweats – 3 out of 5 men (60%) have this, caused by the fall in testosterone levels. It lasts as long as treatment continues for some men. Tell your doctor or nurse if the flushes or sweats are difficult to cope with
  • Decreased interest in having sex (low libido)
  • Breast tenderness and swelling – this occurs in about 3 out of 10 men (30%) and can be distressing. Let your doctor or nurse know if you have this
  • Problems getting an erection (impotence) – this is because you don’t produce testosterone while you have treatment. It gets better for some men within 3 to 12 months of finishing treatment
  • Mild allergic reactions causing itching, skin rashes and a high temperature
  • Painful joints
  • Tiredness and weakness (fatigue) during and after treatment – most people find their energy levels are back to normal within 6 months to a year
  • Headaches – these occur in just over 1 in 10 men (10%)

Occasional side effects

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

  • Bruising, swelling and pain in the area of the injection
  • Anxiety
  • Depression that can be severe and mood changes – let your doctor know if you have this
  • Feeling or being sick – this is usually mild and can be controlled by anti sickness medicines
  • Dizziness – don't drive or operate machinery if you have this
  • Weight gain – you may find you put on weight easily. You may be able to control this with diet and exercise but it can be a struggle to keep weight down when you are having hormone treatment
  • Pain in arms or legs
  • Blurred vision – don't drive or operate machinery if you have this
  • Muscle or bone pain
  • Fluid build up causing swelling in arms, legs or other areas of the body
  • Muscle and bone pain – let your doctor or nurse know if you have this

Rare side effects

Fewer than 1 in 100 people have these.

  • Bone weakening can happen with long term treatment
  • A severe allergic reaction causing fever, chills, shivering (rigors), headaches, and swelling of your lips, face, throat or tongue – let your doctor or nurse know straight away if you have this
  • Ringing in the ears (tinnitus)
  • Changes in blood pressure – during treatment your blood pressure may be lower or higher than usual. Your nurse or doctor will check this regularly. Most people can continue taking triptorelin, and their blood pressure usually goes back to normal either during treatment or when their treatment ends
  • Tummy (abdominal) pain
  • Constipation – drink plenty of fluids and let your doctor or nurse know if you are constipated for more than 3 days
  • Diarrhoea – drink plenty of fluids and let your doctor or nurse know if the diarrhoea continues
  • Severe pain and swelling in the joints of the toes (gout)
  • Muscle cramps
  • Drowsiness
  • Skin rashes
  • Difficulty sleeping
  • Pain in the testicles
  • Shrinking of the testicles
  • Itching
  • Being sick
  • Shaking
  • Gout (severe pain and swelling of the joints, most commonly the big toe)
  • Bigger appetite than usual
  • Muscle weakness
  • Muscle pain
  • Tingling or numbness in fingers or toes
  • Feeling irritable
  • Hair thinning
  • Breathlessness

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.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or 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.


Do not breastfeed during this treatment because the drug may come through in the breast milk.


Related information


More information about triptorelin

This page does not 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: 1 July 2015