This information is about a hormonal therapy called megestrol acetate, that is commonly known as Megace®. It is used to treat breast cancer. The information should ideally be read with our general information about breast cancer or, if appropriate, secondary breast cancer.

Megace is a man-made substance called a progestogen which is similar to the female hormone progesterone. It is a type of drug known as hormonal therapy. Megace is mainly used in the treatment of breast cancer.

The way in which Megace works is not yet fully understood, but it is thought that in some way it interferes with the action of particular female hormones in the body.

Many breast cancers rely on supplies of specific sex hormones, such as oestrogen, to grow. On the surface of the cancer cells are proteins called receptors, which are sensitive to the sex hormones. When the sex hormones come into contact with the receptors, they activate the cancer cells to divide and the tumour grows.

Megace disrupts this process in some way. It may be that it prevents the cancer cells from maintaining the receptors on their surface. Alternatively it may have a more direct way of destroying cancer cells that has not yet been identified.

Your doctor will consider a number of different factors before deciding whether Megace is the most appropriate treatment for you.

For breast cancer, Megace is mainly used as a treatment for women whose cancer has returned after a period of time during which it was successfully controlled with other hormonal therapies such as tamoxifen.

Megace may also be used by women whose cancer has not responded to other hormonal therapies, but whose cancer cells have oestrogen receptors on their surface.

Megace is taken as a tablet. It can be taken up to three times a day, as directed by your doctor. When a single daily dose is prescribed it should be taken at the same time each day – the actual time does not matter. When it is prescribed in divided doses (more than once per day) the doses should be evenly spaced throughout the day.

Each person's reaction to any medication is unique. As people react to drugs in different ways it is not possible to predict who is going to have side effects. Many women who take Megace have no side effects while others will experience them. Very rarely, if side effects are severe, you may have to stop taking the drug and a different hormonal drug may be prescribed.

Usually, there are few side effects of Megace and these are mild:

Increased appetite The most commonly reported side effect is an increase in appetite, causing some people to put on weight. Dieting can help to control this but you should consult your doctor before making any changes to your diet.

Fluid retention Some women have experienced mild ankle swelling caused by fluid retention. This is not harmful but can be uncomfortable.

Feeling sick (nausea) Occasionally people feel sick (nauseated) for the first few weeks of taking Megace, but often the nausea then disappears. Some women find that the nausea continues.

Very rarely, women have reported allergic reactions, jaundice and raised blood pressure.

Like most drugs, Megace should not be taken during pregnancy. Even though women may find that their periods stop while taking Megace it is not a contraceptive, so reliable contraception must be used while having treatment with megestrol.

People with diabetes will need to monitor their blood sugar more closely and may need to adjust their anti-diabetic medication while on treatment with Megace. They should contact their doctor if there are any problems with the control of their diabetes.

Women who have had any form of blood clot or inflammation of a vein should discuss this with their doctor before taking Megace, because it may have an effect on the circulation of blood.

Megace is also sometimes prescribed for the treatment of endometrial cancer (cancer of the womb) and less frequently for cancer of the prostate gland.

It can also be prescribed to reduce hot flushes both in women during the menopause, and for men experiencing hot flushes as a result of treatment for prostate cancer.

As Megace is an appetite stimulant, it can sometimes be helpful for people who have loss of appetite and weight loss due to advanced cancer.

• Keep the tablets in a safe place where children cannot reach them, as Megace 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
• If you are sick just after taking the tablet tell your doctor, as you may need to take another
• If you forget to take your tablet, do not take a double dose. Let your doctor or nurse know. Don't worry, 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 that you 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.
• British National Formulary (54th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2007.

For further references, please see the general bibliography.