SERMs form an oestrogen-like class of drug which is able to bind to oestrogen receptors of one organ system while remaining neutral to others. The SERM used in South Africa to prevent osteoporosis is raloxifene.
Its action is to inhibit bone resorption, while having little or no effect on the breast or endometrium (lining of the womb). It is thought to be particularly effective in preventing fractures of the vertebrae (bones of the spine).
One of the biggest advantages of raloxifene is that it appears to reduce the development of oestrogen-sensitive breast cancers. This means that women who are at high risk of breast cancer can still use this to prevent osteoporosis without the risks inherent in normal HRT.
There are some negative effects though. There is an increased risk to develop thromboembolism (blood clots) and the drug is contraindicated in women who presently suffer from thrombosis, or have a past history of blood clot formation in their veins. Other side-effects are cramps and leg swelling.
The drug has no beneficial effect on vasomotor symptoms such as hot flushes.