For the millions of women who use hormonal contraception in the U.S. (10 million take oral contraceptives alone), the latest study linking the prescription to higher risks of breast cancer is one to keep in mind.
The link made major news back in the '90s, when a review of 56 studies showed that women have a slightly higher risk of breast cancer while taking birth control pills that contain both estrogen and progestin. But for a long time, many doctors and women hoped that because those studied were pills with higher doses of hormones, the modern, low-dose contraceptive pills would be safer.
New research published on Wednesday in the New England Journal of Medicine, the first of its kind, shows that isn't the case.
Researchers at the University of Copenhagen tracked 1.8 million women between the ages of 15 and 49 in Denmark's health registry, in which all filled prescriptions are required to be recorded. They noticed that in a stretch of almost 11 years, women who were currently or recently using contemporary hormonal contraceptives (which include the pill, hormone-releasing IUDs, patches, vaginal rings, injections and morning-after emergency birth control) had a 20 percent higher risk of developing breast cancer compared with those who didn't. The highest risk occurred with those who used Plan B.
The longer women used hormonal contraceptives, the higher their risk, growing from 9 percent for women using it less than a year to 38 percent for those using them for 10 years or more. The risk is smaller for women in their teens, 20s and 30s.
To offer some perspective, that means for every 100,000 women, 68 cases of breast cancer a year developed from those who used hormonal contraceptives and 55 from those who didn't. It's a small risk increase, but still a significant one when you consider that large populations of women are on hormonal contraception.
So, should you be worried? Experts say that really depends on who you are, which is the biggest takeaway from this study. Doctors should talk to patients about the benefits and risks of any contraception before prescribing them birth control.
"Women understand that whatever they do carries risk, and hormonal contraceptives are no exception," Dr. Ojvind Lidegaard, who led the study, tells Time. "We should make individual assessments of the risks and benefits. For some women, it will still be a good choice to take these products for some years. For other women, for example women with a tendency toward depression, we really need to think twice about whether we give them a product that can deteriorate their mental status. The same applies with women who have a genetic predisposition to breast cancer with BRCA genes."
Whether or not one should use hormonal contraceptives really does depend on the individual and her medical and family history.
The study doesn't take into account other factors that could increase the risk of breast cancer, such as how much someone exercises or what that person's alcohol consumption is like. And while there's a link between hormonal contraceptives and an increased risk of suicide attempts, blood clots and now breast cancer, there's also strong evidence that shows benefits including a reduced risk of ovarian cancer, endometrial cancer and colorectal cancers later in life.
If you're concerned and need advice about weighing risks against benefits, talk to your doctor.