Millions of women worldwide have benefitted from hormonal birth control systems since “the pill”—the ubiquitous stand-in for daily contraceptive medication—was first released in 1960. Whether delivered by pill or implant, these medications have minimal immediate side effects, a more than 90% efficacy rate, and can help with severe period-associated cramping, making them life-changing for many women.
So it may be disheartening for those women to hear that a huge new study from Danish researchers suggests that long-term birth control use can marginally increase a woman’s risk of developing breast cancer.
Globally, 13% (roughly 140 million) of women use birth control, Reuters reports. Some opt for the pill, which delivers a combination of progesterone and estrogen, and prevents pregnancy by blocking a woman’s body from releasing an egg and making it harder for sperm to get through her cervical mucus. Women also have the option of having devices inserted into their arms or uteruses to give them a low dose of these hormones over time. Although they have some moderate side effects like headaches, breast tenderness, or intermittent spotting, using hormones to protect against pregnancy been considered relatively safe—especially more modern forms of medication, which deliver lower doses.
Lina Mørch, an epidemiologist at Copenhagen University Hospital in Denmark, and her team have been studying the long-term effect of using hormonal methods of birth control for more than a decade. On Dec. 6, they published (paywall) a new analysis in the New England Journal of Medicine of over 1.8 million women in Denmark aged between 15 and 49. The women had never had any problems with fertility, breast cancer, or blood clots. Over the course of 11 years, Mørch’s team used the country’s hospital and pharmaceutical registries to track who was using hormonal birth control, and who would go on to develop breast cancer. They found that on average, women who were long-term users of any kind of hormone-based birth control were 20% more likely to develop breast cancer than women who weren’t. This translates to one more case per 7,690 women.
“What’s clear from this paper is that the duration of use is important,” says Mørch. The average user in her study was taking the pill for a total of five years. Women who use these types of birth control for more than 10 years had almost twice as many cases of breast cancer as women who used birth control for less than a year, although these results were not statistically significant.
Mørch and her team have conducted several studies on hormonal birth control, including one from last year that linked contraceptives to depression. She doesn’t think that these data necessarily damn the medication. For some, it may still be the best choice—especially if it mitigates the symptoms of painful periods. ”Women are competent in using this in a more nuanced way,” she says. “If you have extreme pain that makes your daily life difficult, then it may be worth it to take the risk.”
But in these cases, women should also work with their health care providers to assess what may be best for them. Women who are at higher risks for breast cancer, like older women or those with a family history of the disease, may want to use alternative forms of birth control, like condoms (which also protect against sexually transmitted infections) or the copper IUD. Doctors should also screen women for mental health concerns.
“Most medication is related to a risk,” Mørch says. When meds are a matter of life or death, this is a more straightforward calculation than meds that improve quality of life. Healthy women don’t have to take these hormones for long periods of time, and may decide that the small increase risk of breast cancer may not be worth it for them.
In the meantime, these results may provide even further incentive for scientists to come up with better birth control options, maybe this time for men.