More evidence that hormone replacement therapy could be harming, not protecting the hearts of older women has been published.
Risks and benefits of HRT have been confused
Research into 5,000 women from the UK, Australia and New Zealand suggests women over 60 are more at risk of heart and blood problems.
The British Medical Journal study backs major US research which revealed risks for millions of women worldwide.
Experts say shorter-term HRT use in younger women is safe and effective.
It is used to alleviate some of the unpleasant symptoms of menopause such as hot flushes and night sweats.
HRT is now very rarely prescribed to older women in the UK.
The WISDOM study began in 1999, and involved doctors at the University of Adelaide in Australia, Wellington School of Medicine and Health Sciences in New Zealand, and the Medical Research Council in the UK.
It identified 5,692 healthy women registered at GP practices with an average age of 63, and randomly gave them either combined oestrogen and progestogen HRT pills, or "dummy" placebo pills.
When the US Women's Health Institute (WHI) study was halted in 2002 after finding significant evidence of HRT endangering the health of some of its patients, the WISDOM study, which was almost identical in its method, was also stopped.
However, researchers were able to analyse the results in the first few years of the trial.
They found, like the WHI study, a significant increase in the number of "major cardiovascular events", such as angina, heart attack or even sudden heart death, and potentially dangerous blood clots in the group given HRT, compared with those given no hormone treatment.
HRT use has declined by 50% in the UK since the WHI study was halted.
Dr Madge Vickers, former head of the MRC General Practice Research Framework, who led the study, added: "Importantly, the WISDOM study showed that there is no overall disease prevention benefit from HRT and some potential risk for women who start hormone replacement therapy many years after menopause.
"However, most women take HRT for relief of menopausal symptoms, and quality of life is an important part of the equation."
Professor John Stevenson, a consultant metabolic physician from the Royal Brompton Hospital in London, and chairman of the charity Women's Health Concern, stressed that, for younger women, HRT was a safe treatment.
He said: "This is a highly effective way of helping women with menopausal symptoms, and it is almost unheard of for much older women to be starting a course of HRT.
"Women in their 50s might be given HRT for a year or two, then weaned off to see if their symptoms have eased."