Two studies have linked hormone replacement therapy with cancer, suggesting - but not yet proving - that HRT can increase the risk of breast and ovarian cancer.
But doctors stressed that younger women who need the drugs to relieve serious symptoms of menopause should still consider taking them because new, lower-dose formulations are available and doctors now know to prescribe them for shorter periods of time.
One study, published in the Lancet medical journal, found women who used HRT were 20 per cent more likely to die from ovarian cancer than similar women who did not use HRT.
Dr Valerie Beral and colleagues at the Cancer Research UK Epidemiology Unit in Oxford, said their findings suggested that that as many as 1,000 extra women in Britain had died from ovarian cancer between 1991 and 2005 because they were using hormone replacement therapy.
They used data from the "Million Women Study," which looked at just under a million women, about half of whom were current of former HRT users. For every 1,000 women who used HRT for five years, 2.6 developed ovarian cancer. That compared to 2.2 cases of ovarian cancer for every 1,000 women who did not use HRT.
"The effect of HRT on ovarian cancer should not be viewed in isolation, especially since use of HRT also affects the risk of breast and endometrial cancer," Dr Beral's team wrote.
"The total incidence of these three cancers in the study population is 63 percent higher in current users of HRT than never users," they added. "Thus when ovarian, endometrial and breast cancer are taken together, use of HRT results in a material increase in these common cancers."