A major study which cast doubt on the safety of hormone replacement therapy may have been flawed, say scientists.
There is confusion over the effect of HRT
The US Women's Health Initiative research found HRT use increased the risk of heart attacks and strokes.
The study, involving 16,000 women was stopped three years early in 2002, and many women were scared off using HRT.
However, Yale University scientists now say design flaws meant that study could not have detected any positive impact of HRT on heart health.
It is estimated that 340,000 British women have stopped taking HRT since the negative publicity.
It had been widely thought that a common form of HRT using the female sex hormones oestrogen and progesterone could help protect against heart attacks and stroke.
The WHI study seemed to suggest the reverse was actually the case.
However, the new research, led by Dr Frederick Naftolin, argues the study was too small to draw any statistically meaningful conclusions.
It says most women in the study were in their 60s and 70s, whereas previous research had suggested HRT provided protection from heart disease for women in their early 50s.
Separate research had also indicated that the heart benefit of HRT was lost if treatment was delayed until years after the start of the menopause.
Even the youngest women in the study had gone at least a year without a period, and most had gone many years.
The Yale team said more research was needed to pin down the exact effect of HRT on heart disease - and that it would be wrong to dismiss the idea that it could prevent heart attacks and stroke.
Dr John Stevenson, of the British Menopause Society, said conflicting research had served only to confuse and frighten women off taking HRT.
"We had two reasons to give HRT; for relief of menopausal symptoms and for the prevention of osteoporosis.
"We knew that there was a small risk of breast cancer and a very very small risk of blood clots, but the benefits far outweighed the risks. And nothing has changed at all."
"This whole issue has been a huge disservice to women. Women have suffered
unnecessarily because of this."
Karen Winterhalter, of Women's Health Concern, said the number of new HRT prescriptions was down by a million this year.
She said the WHI study - and the later "Million Women" trial which highlighted
the increased risk of breast cancer - had had a huge impact.
She said: "We and others have been saying all along that the WHI didn't recruit the
right type of women."
In February, Professor Susan Johnson, of the University of Iowa, a WHI investigator, said the study's message had been widely misunderstood, and that HRT was effective treatment of women with severe menopausal symptoms.
The research is published in the journal Fertility and Sterility.