Taking the contraceptive pill does not increase a woman's chances of developing cancer and may even reduce the risk for most women, finds a major British study.
However, there was an increased risk for women who used it for more than eight years.
Researchers at the University of Aberdeen studied the records of 46,000 women over 36 years, half of whom took birth control pills at some time and half who had never taken it.
Researchers, led by Professor Philip Hannaford, found that "there was no overall increased risk of cancer among pill users" and that taking the pill could cut the risk by up to 12 per cent over a woman's lifetime in those who had taken the pill for eight years of less.
A 12 per cent reduction works out to about one fewer case of cancer for every 2,200 women who used the pill for at least a year, reports the study, published in the British Medical Journal.
The evidence also suggested that women were protected from the risk of developing cancers for at least 15 years after stopping the pill.
In particular, those who had taken the contraceptive pill had statistically significant lower rates of bowel and rectal cancer, as well as uterine and ovarian cancer.
Since its introduction in the early 1960s, more than 300 million women around the world are thought to have used oral contraception.
Although several studies have looked at the overall balance of cancer deaths associated with oral contraceptives, none had ever examined the absolute risks, the authors say.
The authors note that their results may not be applicable to all countries.
"The balance of cancer risks and benefits, however, may vary internationally, depending on patterns of oral contraception usage and the incidence of different cancers," they write.
