The average woman in the UK can expect to spend half her adult life after the menopause. In theory, hormone replacement therapy (HRT) returns the female body to the metabolic equivalent of the prime of youth. Icons such as Cher and Helen Mirren continue to grace the silver screen wearing next to nothing when they are rising 60, giving substance to the rumour that it's possible to remain firm of breast, trim of heel and bright of eye by knocking back a capsule of the missing hormone every morning.

In practice, around half of women never try HRT and half the rest abandon it because of side effects. The political philosopher Foucault (in common with radical feminists like Germaine Greer) described the HRT industry as one of medicine's greatest con-tricks. Doctors and pharmacists, they say, have persuaded women that their natural ageing process constitutes an illness that needs to be investigated and controlled by male-dominated professions.

Leaving sexual politics aside, what are the facts of the condition? The problems can all be traced to the ovary, which stops producing the female hormones, oestrogen and progesterone, at around the age of 50. If the ovary simply died quietly, the transition might not be too bad, but it tends to go out with a bang, with a massive release of oestrogen every few days, leading to a harmless but dramatic 'hot flush'. Hot flushes are often quite tolerable if you are pottering about at home - as many women of a certain age will tell you, just sit down in a cool breeze until it passes - but the same symptoms in a high-pressure and socially-exposed work environment can leave you feeling exhausted and humiliated. Around 75% of women experience hot flushes, along with sweats, mood swings and waves of tiredness.

Even when the menopause itself is over (and that can take a year or two), low levels of female hormones will have persisting knock-on effects. The bones, for example, become unable to retain calcium effectively (a condition known as osteoporosis), and the risk of fractures ( especially wrists, ankles and hips) increases year on year. The 'dowager's hump' that characterised so many elderly women three decades ago was due to recurrent osteoporotic fractures of the thoracic vertebrae.

If your mother or grandmother had a dowager's hump you are at increased risk of osteoporosis yourself. Your GP might suggest a bone density scan to assess your current status, and another one in three years to gauge the rate of decline. Bone density testing generally involves an injection of a radioactive substance, so don't ask for one too often - but if your decision to take HRT or not hangs on this question alone, it may be worth the exposure. Not all districts offer bone density testing on the NHS, but a private scan can be arranged if you are prepared to pay for it. A newer method of bone density assessment - ultrasound - is much less invasive but not yet proven to be as accurate.

Every woman is different, but on average you can expect a dramatic reduction in acute menopausal symptoms like hot flushes and mood swings if you take regular HRT. There is also no doubt whatsoever that 'medical' HRT (as opposed to the totally unproven remedies sold in health food shops) reduces your chance of developing osteoporosis. A few years ago it was thought that HRT also had a beneficial effect on cholesterol levels and the risk of heart disease, but the latest research suggests that there is no such effect, or that if there is one, it is small.

Apart from a risk of getting your periods back temporarily, the most common side effects of HRT are bloating, weight gain, and swollen, tender breasts. None of these will kill you, but you would have to tolerate them day in, day out for the duration of the treatment. As in the contraceptive pill, the hormones in HRT can be combined in different proportions, and it can take three or four trial runs (with tablets and/or patches) to find the best combination for any particular woman. Just because your sister-inlaw put on weight with preparation X does not mean that you will - try it and see. Some more modern preparations (based on entirely artificial hormones) come with the promise that you won't see a return of your periods, but you might prefer to take a hormone your womb would recognise as the genuine article.

In terms of safety, there is little to choose between the preparations on the market. There is a risk of womb (endometrial) cancer with any oestrogen if taken on its own, but not if it is taken in combination with progesterone for part of every month (hence the relatively complex regimens around a monthly cycle). If you have had a hysterectomy you are safe taking oestrogen alone. There probably is a slightly increased absolute risk of breast cancer with HRT, perhaps two or three in a hundred over and above the risk you would have had anyway (which is around one in 10).

In other words, if you take 100 British women and give none of them HRT, around 10 will get breast cancer at some stage. If you give all of them HRT (and they all keep taking it), 12 or 13 of them will get breast cancer but 10 would have got it anyway. For more on this risk, see the recent article by Jennifer Dixon in the British Medical Journal (http://bmj.com/cgi/content/full/323/7326/1381).

In summary, HRT is more likely to make you feel like Barbara Windsor in the wrong sized bra than Cher in a thong. But it will make the menopause more physically and emotionally tolerable, and make you less likely to need a Zimmer frame when you're 90. Whether that's worth a tablet a day (or two patches a week) from the age of 50 is something only you can decide.