Hindsight is a wonderful thing, the saying goes. And that certainly seems to be the case when it comes to Hormone Replacement Therapy.
In 2002, a huge study of women taking HRT in the US found that the therapy could increase the risk of breast cancer, heart attacks and strokes. This sent a shock wave around the world.
Back in 2002, everyone agreed that HRT prevented some diseases like osteoporosis, as well as relieving symptoms of menopause.
But the new evidence about the risks of cancer (backed up by British research a year later showing an increased risk of ovarian cancer) convinced probably millions of women not to choose HRT.
But now some of the doctors involved in that study are looking back - with regrets.
For example, Dr. Robert Langer, was a principal investigator of the study at the University of California, San Diego.
He says that the 2002 study was set up to see whether those known protective effects of HRT applied to older women too.
It uncovered higher risks of cancer, heart attacks and strokes. But that was in older women.
Those results he says were "were wrongly generalised " to younger women. As a result, women approaching menopause were put off HRT.
He says: "Overgeneralising the results from the women who were - on average - 12 years past menopause to all post menopausal women has led to needless suffering and lost opportunities for many."
HRT has been one of the most bitter medical debates of the last decade.
Currently the NHS's advice is "Most experts agree if HRT is used on a short-term basis (no more than five years), benefits outweigh associated risks.
If HRT is taken for longer, particularly for more than 10 years, you should discuss your individual risks with your GP and review them on an annual basis."
But some doctors, like consultant gynaecologist Nick Panay, are concerned that the message isn't getting through.
He told me he thinks many GPs are still not recommending HRT because of the 2002 research and haven't caught up with the reappraisal.