This information is about a hormonal therapy called cyproterone, which is also commonly called Cyprostat®. It is used to treat prostate cancer. The information should ideally be read with our general information about prostate cancer.

Cyprostat is a type of hormonal therapy that is used in the treatment of prostate cancer.

There are several different types of hormonal therapies. Your doctor can discuss with you which is best for your situation.

Hormonal therapies interfere with the production or action of particular hormones in the body. Hormones are substances produced naturally in the body. They act as chemical messengers and help to control the activity of cells and organs.

Most prostate cancers need supplies of the male hormone testosterone to grow. Testosterone is produced by the testes and adrenal glands. On the surface of prostate cancer cells are proteins called receptors. Cyprostat has a structure similar to testosterone. It attaches itself to the receptors on the surface of the prostate cancer cells, which prevents the attachment of testosterone. Without testosterone, the cancer cells either grow more slowly or stop growing altogether.

Cyprostat is a tablet which is taken two or three times a day. The tablets should be taken after meals and swallowed whole with a drink of water. Doses should be evenly spaced throughout the day.

Cyprostat may be given on its own to treat prostate cancer if other treatments, such as surgery, are not suitable. It is also used to help prevent tumour flare, which can occur when other hormonal-therapy drugs used to treat prostate cancer (known as LHRH analogues) are given. When LHRH analogues are given, there may be a temporary increase in testosterone levels in the first few days or weeks. This may cause an increase in symptoms such as bone pain or difficulty passing urine. This is known as tumour flare and Cyprostat can help to prevent these symptoms occurring.

Cyprostat may also be given to help reduce hot flushes in men who are having LHRH analogues, or who have had their testicles removed (orchidectomy) as part of their treatment.

Each person's reaction to any medication is different. Many people have very few side effects with Cyprostat, while others may experience more. The side effects described in this section will not affect everyone and may be different if you are having more than one drug.

We have outlined the most common side effects. However, we have not included those that are very rare and therefore extremely unlikely to affect you. If you notice any effects that you think may be due to the drug, but which are not listed in this information, please discuss them with your doctor or nurse.

You will see your doctor regularly while you have this treatment so that they can monitor the effects. This information should help you to discuss any queries about your treatment and its side effects with your doctor or nurse, as they are in the best position to help and advise you.

Some people may have some of the side effects listed below:

Breast tenderness or fullness Some men may notice slight breast swelling and tenderness, known as gynaecomastia. Your doctor can advise you about how this can be treated or prevented.

Tiredness You may feel less energetic than usual and it is important to take time to rest. The tiredness usually subsides when the treatment is stopped.

Breathlessness You may have a feeling of mild breathlessness while you are taking Cyprostat treatment. This will disappear if the treatment is stopped.

Feeling sick (nausea), being sick (vomiting) and diarrhoea These effects are rare and are usually mild and easily controlled. Nausea can sometimes be relieved by taking the tablet with food.

Changes in sexual function You may have loss of sex drive (libido) or erection difficulties (impotence). These side effects may continue for as long as you are taking Cyprostat but they should improve after you stop taking the drug. Let your doctor know if you have any of these side effects, as they can prescribe medication to help.

Mood changes You may experience mood swings or feel anxious. Talk to your doctor if this continues.

Blood clot (thrombosis) Cyprostat may increase your risk of getting a blood clot. Let your doctor know if you have a history of blood clots, sickle cell anaemia or diabetes. These conditions can increase your risk of getting a clot.

Effect on liver function Your doctor will take blood samples to test how well your liver is working, as Cyprostat can sometimes cause the amount of particular chemicals produced by the liver to change. If this happens, the drug will be stopped and the liver function will return to normal.

Change in blood-sugar levels If you are diabetic, your blood-sugar levels may be slightly higher than usual and may need more regular monitoring. Your GP or diabetes doctor should be able to help you manage this. Your blood-sugar levels should return to normal after you finish treatment with Cyprostat.

Your doctor will discuss the length of treatment that they feel is appropriate for your situation. Cyprostat is given for as long as it is effective in controlling your cancer. This may be for several months or years.

• It's advisable not to father any children while you are being treated with Cyprostat (as the developing foetus may be affected) so use effective contraception.
• Keep the tablets in a safe place out of the reach of children, as Cyprostat could harm them.
• If your doctor decides to stop the treatment, return any remaining tablets to the pharmacist. Do not flush them down the toilet or throw them away.
• Don't worry if you forget to take your tablet. Do not take a double dose. The levels of the drug in your blood will not change very much – but try not to miss more than one or two tablets in a row.
• Remember to get a new prescription a few weeks before you run out of tablets. Make sure you that have plenty for holidays.

This section has been compiled using information from a number of reliable sources, including:

• Martindale: The Complete Drug Reference (35th edition). Sweetman et al. Pharmaceutical Press, 2007.
• electronic Medicines Compendium (eMC) emc.medicines.org.uk (accessed 25 November 2008)
• British National Formulary (56th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2008.

For further references, please see the general bibliography.