Triptorelin (Decapeptyl SR, Gonapeptyl Depot)

Triptorelin is a hormone treatment for prostate cancer or early breast cancer Open a glossary item.

You might have triptorelin for prostate cancer that is:

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

You might have triptorelin for early breast cancer with other hormone treatments Open a glossary item if you have not had your menopause Open a glossary item (pre menopausal).

You might also have triptorelin as part of a clinical trial for prostate or breast cancer.

How does triptorelin work?

Triptorelin is a gonadotrophin releasing hormone (GnRH) blocker. This means it stops messages from a part of the brain called the hypothalamus that tells the pituitary gland Open a glossary item to produce luteinising hormone.

Luteinising hormone tells the testicles to produce testosterone Open a glossary item. So, blocking GnRH stops the testicles producing testosterone. 

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

In women, it stops the ovaries Open a glossary item 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 do you have triptorelin?

You usually have triptorelin as an injection into a muscle (usually in your buttock). If you're having the version Gonapeptyl Depot, you can have this under the skin of your tummy.

How often do you have triptorelin?

You might have it either

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

The length of time you continue this treatment for depends on your cancer type. Your nurse or doctor will go through how long to expect taking triptorelin.


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.

What are the side effects of triptorelin?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

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

If you are having triptorelin for prostate cancer you might have an increase in symptoms after your first injection. 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.

Abnormal sensations of the skin

You might have unusual skin sensations such as numbness, tingling, prickling or burning. It can feel like pins and needles. 

Symptoms are more common when you first start treatment. These symptoms can get worse before they get better. 

Let your doctor or nurse know if you have this.

Pain in different parts of the body

You might have pain in different parts of your body such as your back, muscles, pelvis Open a glossary item or tummy (abdominal) during treatment.

Less commonly you might have pain in your joints, legs or arms (extremities). Some men might have pain when passing urine.

Rarely you get pain in your testicles or breasts. You might also have muscle cramps.

Let your healthcare team know so they can advise you on how to help 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, injections or pellets. Your doctor or nurse can refer you 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.

Vaginal problems

You might have dryness, bleeding from the vagina or your periods might stop. This treatment might make the ovaries overactive. This is called ovarian hyperstimulation syndrome or ovarian hypertrophy. You might have pelvic pain, bloating, diarrhoea or feeling or being sick. Let your team know if you have these symptoms.

Pain during or after sex

Talk to your treatment team if this is a problem for you.

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:

  • an allergic reaction that can cause a rash, shortness of breath, redness or swelling of the face and dizziness - some allergic reactions can be life threatening, alert your nurse or doctor if notice any of these symptoms
  • headaches
  • dizziness
  • bruising, inflammation or tenderness at the injection site
  • changes in mood such as feeling very low (depression)
  • feeling sick
  • weight gain, or rarely weight loss
  • fluid build up in different parts of the body (oedema)
  • blood pressure changes such as high blood pressure, rarely it might drop
  • breast swelling
  • feeling irritable

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:

  • dry mouth
  • blurred vision
  • ringing in the ears (tinnitus)
  • diarrhoea
  • constipation
  • pain and swelling in the joints usually the big toe (gout)
  • high levels of fat in the blood – you will have regular blood tests to check for this
  • hair thinning
  • cough or breathlessness
  • lowered or increased appetite
  • high blood sugar levels (diabetes)
  • difficulty sleeping (insomnia)
  • skin problems such as a rash, acne, redness or itching
  • urine problems such as needing to pass urine at night or difficulty completely emptying your bladder when passing urine
  • kidney changes – you will have regular blood tests to check for this
  • liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working
  • feeling your heartbeat in your chest (palpitations)
  • high temperature with severe shivering (rigours)
  • feeling very drowsy
  • testicles getting smaller (called testicular atrophy)
  • asthma getting worse if you already have asthma
  • blood clots that can be life threatening; signs are pain, redness and swelling where the clot is. Feeling breathless can be a sign of a blood clot in the lung. Contact your advice line or doctor straight away if you have any of these symptoms

Other side effects

Long term treatment with triptorelin can increase the risk of bone thinning (osteoporosis). This means the bones become more brittle and increases the risk of them breaking (fracture). There isn't enough information to work out how often this side effect might happen.

You might have a bone density scan to check the strength of your bones. You might also have medicines to help strengthen the bones.

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 medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Pregnancy and contraception

This treatment might harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you're having treatment and for a few months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment.


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

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

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

  • Electronic Medicines Compendium 
    Accessed October 2022

  • Early and locally advanced breast cancer: diagnosis and management
    National Institute for Health and Care Excellence (NICE), July 2018 

  • Prostate cancer: diagnosis and management
    National Institute for Health and Care Excellence (NICE), May 2019. Last updated 2021

Last reviewed: 
01 Nov 2022
Next review due: 
01 Nov 2025

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