Cyproterone acetate (Cyprostat)

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Your doctor has recommended a medication called Cyprostat as treatment for your prostate cancer. This page provides extra information about your medicine, summarises possible side effects and methods to alleviate them.

What is in Cyproterone acetate Cyproterone acetate is an oral tablet taken at a dose of 100mg three times a day, and belongs to a group of medicines called testosterone antagonists. They are used to treat male patients with prostate cancer. Many people like to take it at the same time each day – the actual time does not matter. Some prefer to take it with food, some after meals  - try to find a convenient time and stick to it as it's easier to remember to take the tablets in the long term.

How do they work? Some tumours such as prostate cancer are stimulated by the body's own male hormone (testosterone). Stopping the body's testosterone reaching the tumour can cause cancer cells to stop growing and in some cases shrivel up and die completely (self-destruct - (apoptosis)). Cyprostat works by fooling the signal pathway between the brain (pituitary) and the testes by increasing the blood levels of another hormone which looks similar to a sex hormone. In turn the brain thinks they are producing too many hormones, including testosterone, and as a consequence switches off the driving signal by itself - this results in reducing the blood level of testosterone. Another way Cyprostat works is by interfering with the cancer cells ability to read testosterone in the blood stream. Cancer cells have receptors in the same way as a TV needs an aerial. If the aerial is damaged the TV can't show a clear picture. In the same way, if the receptor on the cell is blocked it can't be influenced by the body's hormones..

How will I & the doctor know they are working? In most cases there is something the doctor can measure. This may be how you feel, a symptom related to your cancer, something which can be felt on examination (e.g. a lump or size of prostate), something seen on a scan or x-ray, or a blood test called PSA (the level of which will get lower if you are responding).

Possible side effects All medications have side-effects. These can affect some people more than others. It is hard to predict the level and type of side-effect for each individual. Listed below is an overview of the more common side-effects you may encounter. However, you may experience none, all, or only a few of these. You may also have a rare side-effect not listed here. If you become aware of any other side-effects, please report them to your clinic staff. 

• A feeling of depression.  It is common to have a change in mood with Cyprostat and this may lead to, or exacerbate, depressive illness in some cases.

• Damage to the liver. Occasionally Cyprostat can interfere with the function of your liver. This is rarely more than very mild but if you have a pre-existing liver condition you must tell your doctor. If you feel unwell or develop yellow jaundice, stop the Cyprostat immediately.

• Lethargy. It is possible to have mild lethargy with Cyprostat. It is most severe at the beginning but can wear off over time.  In some men it occasionally has the opposite effect and they experience wakefulness.

• Nausea and indigestion.  Feelings of mild sickness (nausea) and indigestion can occur but it usually wears off after a few weeks.  

• Weight gain. Weight gain can be a side-effect of Cyprostat and this is sometimes due to water retention. At other times it is a consequence of eating more either due to an increased appetite, or mild nausea "to settle the stomach". 

• Ankle swelling. If prone to this, Cyprostat can make it worse. In severe cases this can lead to fluid retention, a strain on the heart, an increased risk of angina and heart failure.

Less common side effects include:-

Other issues There is no interaction between Cyprostat and moderate amounts of alcohol. Cyprostat does not usually affect your ability to drive.

Further general information Your doctors and specialist nurses are in an ideal position to give you relevant information on your disease and treatment as they know your individual circumstances. Cancerbackup has a help line (0808 800 1234) and a prize winning video available in English, Italian, Urdu, Bengali, Gujarati & Hindi explaining Radiotherapy & Chemotherapy. Cancernet.co.uk has over 500 pages describing cancer, its management, practical tips and tool which patients, their carers and their doctors have found helpful during the cancer journey.