US: Women on the birth-control pill have surprisingly lower risks of heart disease, strokes and breast cancer, according to the largest women's health study ever done.
The findings by the Women's Health Initiative in the US - the biggest study of oral contraceptives - are contrary to what many previous studies have found.
Results from nearly 162,000 participants were presented at an American Society for Reproductive Medicine conference in Philadelphia.
The same US study that led millions of women to abandon the use of hormones after menopause now provides reassurance that the pill is safe.
Doctors say the type of hormones and the stage of life when they are used may be what makes them helpful at one point and harmful at another.
"We're still learning more and more about the biology," said one of the researchers, Dr Michael Diamond of Wayne State University in Detroit.
About 16 million American women currently take birth control pills, and hundreds of millions have used them since they first came on the market in 1960. Most combine synthetic forms of oestrogen and progestin in various doses.
Women taking these hormones after menopause were more likely to have heart disease and certain cancers, a finding that prompted part of this study to be stopped in 2002. Previous research on oral contraceptives suggested that they, too, raised the chances of heart disease.
But the new study found the opposite: lower risk of heart attacks, strokes, high cholesterol, high blood pressure and other heart-related problems among the 67,000 women in the study who had ever taken the pill.
Women on the pill also had a 7 per cent lower risk of developing any form of cancer, a small benefit that increased with length of use, Dr Rahi Victory of Wayne State said.