The way in which toremifene works is not yet fully understood but its main function is as an anti-oestrogen drug. This means that it interferes with the action of the female hormone oestrogen.

Most breast cancers need supplies of the female sex hormone oestrogen to grow. Cancer cells have proteins called receptors on their surface that the sex hormones attach to. Cancers with oestrogen-receptors on the surface of their cells are called 'oestrogen-receptor-positive' (ER-positive) and toremifene is most effective against these cancers.

Under normal circumstances, when oestrogen comes into contact with the receptors it fits into them and activates the cancer cells to divide so that the tumour grows.

Toremifene imitates the action of oestrogen and fits into the receptor but does not activate the cells to divide. The toremifene remains in place and prevents oestrogen from reaching the cancer cells so that they either grow more slowly or stop growing altogether.

Each person's reaction to any medication is different. Many women who take toremifene have no side effects, while others will experience them. We have outlined the most common side effects so that you can be aware of them if they occur. However, we have not included those that are very rare, and which are 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 women may have some of the following:

Hot flushes and sweats Sometimes the flushes will gradually lessen over the first few months but some women continue to have them for as long as they take toremifene.

There are a number of ways to help to reduce or control hot flushes and sweats. Some women find it helpful to avoid or cut down on tea, coffee, nicotine and alcohol.

Recent research suggests that progesterone or some anti-depressants may be helpful in controlling this side effect. Your nurse or doctor can discuss this with you.

Some women find that complementary therapies help. Your GP may be able to give you details about obtaining these on the NHS.

Nausea and indigestion Feelings of sickness (nausea) and indigestion are fairly common but can often be relieved by taking your tablet(s) with food or milk or at night. Although nausea is quite common initially, it usually wears off after a few weeks.

Thrombosis (blood clots) This is very rare. Signs of a thrombosis include pain, warmth, swelling or tenderness in an arm or leg, or chest pain. Any of these signs must be reported to your doctor immediately.

Vaginal bleeding or discharge Let your doctor know if you have any vaginal bleeding or discharge.

Vision problems Blurred or reduced vision is again very rare but any visual changes should be reported to your doctor.

Tumour flare Women who are prescribed toremifene for advanced cancer, where it has spread to the bones, may experience something called tumour flare when they start taking toremifene. This can cause a raised level of calcium in the blood (hypercalcaemia) with symptoms of nausea, vomiting and thirst. Very occasionally, a short stay in hospital is necessary until the calcium levels have been reduced.

There is some evidence suggesting that while taking toremifene it can lower the level of fat or lipids in your blood (high levels of fat or lipids in the blood contribute to heart disease). It is thought possible that toremifene may be more effective than tamoxifen in helping to prevent heart disease. It is also thought that toremifene may help to prevent bone loss, which can reduce the risk of osteoporosis (thinning of the bone) in some women.