If you want to avoid an unintended pregnancy, taking birth control is usually a no-brainer. But what if that same birth control upped your risk of breast cancer?
According to research published in The New England Journal of Medicine, women who take hormonal birth control pills or use hormonal IUDs for years experience a small yet significant increase in their risk of breast cancer compared to those who don’t.
The study followed 1.8 million Danish women for more than 10 years and found that, for every 100,000 women, hormonal birth control caused an extra 13 cases of breast cancer a year. Specifically, there were 55 breast cancer cases each year among the 100,000 women who didn’t use hormonal birth control, and 68 cases of breast cancer among those who did.
The study didn’t find any big distinctions between the hormonal method women used—those who used combined oral contraceptives (which use estrogen and progestin) and those who used progestin-only methods each had a higher risk. Ditto for whether women used a hormonal IUD or took a pill. A woman’s risk went up the longer she used hormonal birth control, the study found. So, obviously, hormones are to blame for the increased risk, but the exact mechanisms aren’t yet known.