Triptorelin (Decapeptyl SR, Gonapeptyl Depot)

Triptorelin is a hormone drug that you might have as a treatment for prostate cancer that is:

  • advanced (spread to other parts of your body)
  • locally advanced with or without radiotherapy or surgery

Researchers are also looking into using triptorelin as a treatment for breast cancer. 

How it works

Triptorelin is a gonadotrophin releasing hormone blocker. This means it lowers the level of testosterone (the male sex hormone). It stops the release of lutenising hormone from the pituitary gland. 

Prostate cancer depends on testosterone to grow. So triptorelin can shrink the cancer or slow its growth. 

In women, it stops the ovaries from producing oestrogen.

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 it

You have triptorelin as an injection either

  • into a muscle (usually in your buttock)
  • just under the skin of your tummy

When you have it

You might have it either

  • once a month
  • every 3 months
  • every 6 months


You have blood tests before and during your treatment. They 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.

Temporary side effects

You might have an increase in symptoms after your first dose of this drug. This may carry on for a few weeks. This is called tumour flare. So your doctor might give you another type of hormone drug to prevent the symptoms of tumour flare. 

Symptoms of tumour flare include:

  • increased pain or difficulty passing urine 
  • bone pain
  • back pain
  • blood in your urine 
  • a feeling of pins and needles in your legs 

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 and sweats 

Menopausal symptoms can be difficult to cope with. They include:

  • hot flushes
  • reddening of the skin
  • sweating
  • a racing heart (palpitations)
  • feeling anxious, irritable or panicky

Talk to your doctor if your symptoms are hard to cope with.  They might be able to prescribe medicine. We also have tips on how to cope with them.

Weakness or loss of sensation in your legs

This may happen if your cancer has spread into your bones, Symptoms are more common when you first start treatment, when symptoms can get worse before they get better. 

Tell your doctor or nurse straight away if you have this. 

Back or muscle pain

You might have muscle pain during treatment. Let your treatment team know so they can advise you on how to reduce it.

Loss of sex drive (libido)

Low testosterone levels can lower your interest in sex. 

It can help to talk this through with your partner. You can still feel close to each other through cuddling and kissing. It may also help to talk to a counsellor or therapist. Your doctor or nurse can organise this for you.

Erection problems 

You might have problems getting an erection (impotence). This may get better within 3 to 12 months after the treatment ends. 

Talk to your doctor or nurse if you have problems getting an erection. There are treatments that can help, such as medicines, vacuum pumps, and injections or pellets. Your doctor or nurse can refer to a sex therapist. 

Tiredness and weakness (fatigue)

Tiredness and weakness (fatigue) can happen during and after treatment - doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.

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:

  • allergic reaction
  • headaches and dizziness
  • bruising or tenderness at the injection site
  • depression
  • feeling sick
  • weight gain
  • swollen hands and feet (fluid build up)
  • blood pressure changes

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:

  • breast swelling
  • aching joints
  • blurred vision
  • bone thinning
  • ringing in the ears (tinnitus)
  • diarrhoea
  • constipation
  • swelling in the joints of the toes (gout)
  • pain in your testicles
  • hair thinning
  • cough or breathlessness
  • aching muscles
  • tummy (abdominal) pain

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.

Pregnancy and contraception

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


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

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.

This page is due for review. We will update this as soon as possible.

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