Cyproterone acetate (Cyprostat)

Prostate cancer depends on the male sex hormone, testosterone, to grow. The aim of hormone therapy for prostate cancer is to reduce or stop the body making testosterone, or to block testosterone from reaching the cancer. This can slow down or shrink the cancer.

Cyproterone acetate is a type of hormone therapy drug called an anti androgen. Androgens are male sex hormones, and testosterone is an androgen. Prostate cancer cells have receptors on them that take up testosterone, which stimulates the cells to grow and divide. Anti androgens such as cyproterone attach to the testosterone receptors and stop testosterone reaching the cancer cell. 

You can take cyproterone acetate either on its own, or with another type of drug for prostate cancer called a luteinising hormone (LH) blocker. LH blockers include goserelin (Zoladex), leuprorelin (Prostap) and triptorelin. If you are having cyproterone acetate with one of these drugs, it is to stop what is called a flare reaction. When you first start taking LHRH blockers you actually make more testosterone for the first few days or weeks. This soon settles down, and after a few weeks you stop making testosterone. Cyproterone acetate helps reduce any cancer symptoms caused by this temporary increase in testosterone.

You take cyproterone acetate as a tablet 2 or 3 times a day, after meals. Try to take it at evenly spaced times during the day. If you are having it to stop a flare reaction, you take it for a few days before starting the luteinising hormone blocker, and stay on it for about 4 to 6 weeks.

It is very important that you take tablets according to the instructions your doctor or pharmacist gave you. Whether you have a full or empty stomach, for example, can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

There is general information about hormone therapies in the cancer treatment section.

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

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

• Decreased interest in having sex (libido) and problems getting an erection (impotence) – this usually improves after you finish treatment
• Breast tenderness and swelling – this can be distressing. Rarely, you may have some discharge from your breast (galactorrhoea) with the swelling
• Feeling sick – this is usually very mild and can be controlled by anti sickness drugs
• Cyproterone acetate may have a harmful effect on a developing baby – you are advised not to father a child while you are on treatment. If you are sexually active you should discuss contraception with your doctor or nurse before you start your treatment
• You may not be able to father a child immediately after treatment with this drug. However, this is usually temporary. It is important to talk to your doctor before starting treatment if having a baby is important to you

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

• Tiredness or fatigue – this usually improves within a few weeks of starting treatment
• Sadness or depression – this usually improves within a few weeks of treatment. If it goes on for longer, talk to your doctor or nurse about getting some help
• Fluid retention causing ankle and or finger swelling

Fewer than 1 in 100 people have these.

• Changes in how your liver works – you will have blood tests to check for this. Your liver nearly always goes back to normal after treatment ends
• Reduced number of red blood cells (anaemia)
• Dry skin, and a rash
• Breathlessness
• Blood clots – there is a slightly increased risk of developing a blood clot (thrombosis) when you are taking cyproterone. If you’ve had a blood clot in the past you should tell your doctor. They may want to change you to another type of hormone therapy
• There is a small risk of developing a type of brain tumour called a meningioma if you take cyproterone acetate for a long time.  If you have had a meningioma or you develop one you should not take this drug

If you have diabetes, cyproterone acetate may affect your blood sugar levels. You should check your blood sugar more often when you are having  cyproterone.

The side effects above 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)
• Other drugs you are having

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

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