Do hormonal birth control pills raise breast cancer risk?

About 1 in 7 women between ages 15 and 49 in the United States use hormonal birth control pills, according to the Centers for Disease Control and Prevention. Millions more use other hormonal contraceptives, such as injections and hormonal IUDs.

Some research suggests a link between birth control pills and a higher risk of breast cancer. One major example is a large 2017 study published in The New England Journal of Medicine (NEJM). Researchers found that women who used hormonal birth control had a 20 percent increased risk. While earlier studies focused on older forms of hormonal contraception, the NEJM study examined newer forms, which experts believed would be safer.

It's critical to understand: Breast cancer risk is low overall for people who use hormonal birth control. Still, studies like the one published in NEJM can be alarming, so it's essential to look at how the research was conducted, and what findings like this really mean for your health.

How the study was done

Researchers followed 1.8 million Danish women between the ages of 15 and 49 for about 11 years, tracking their use of hormonal birth control, including pills, patches, vaginal rings, certain IUDs and Plan B (the morning-after pill). To reach their conclusions, they did not include women who had been treated for infertility, or who had a previous diagnosis of cancer or venous thromboembolism.

There were limits to the study in that researchers considered some risk factors for breast cancer—including childbirth, education, and family history—but not others. They did not adjust for alcohol consumption or physical activity, for example. The group studied was made up exclusively of Northern Europeans, as well, meaning the results may not translate to other populations.

What they found

During those 11 years, there were 11,517 cases of breast cancer among the Danish women. Overall, those who currently or recently used hormonal contraceptives were 20 percent more likely to be diagnosed with the disease than those who didn't.

It appeared that the longer women were on hormonal birth control, the greater their chances of breast cancer. Their risk increased by 38 percent if they had been using a hormonal contraceptive for more than 10 years, but rose by only 9 percent if they used it less than a year. If women used it at least five years and then stopped, their chances remained elevated five years later.

Breast cancer risk also differed by age. Most of the increase occurred in women in their late 30s and 40s, and there was very little raised risk for women under age 35. Breast cancer risk peaks between the ages of 50 and 70, and past hormonal birth control use is thought to have little lasting impact at this age.

What that really means

While the statistics may have seemed dire, they should be considered in terms of absolute numbers—or how many more women are diagnosed with breast cancer each year. That 20 percent increase works out to about 13 additional women per every 100,000.

In other words, for those aged 15 to 49 who didn't use hormonal birth control, there were about 55 cases of the disease for every 100,000 women. For those who did, the incidence was 68 per 100,000. It's 1 additional diagnosis for every 7,690 women.

What's more, the raised breast cancer risk largely affected women 35 and older—mostly in their 40s. For women under 35, whose odds are very low to begin with, the increase worked out to just 1 additional case per 50,000 women.

What that means for you

Younger women using hormonal birth control should have little reason to worry. It’s still widely considered to be safe and effective. Not only does it prevent pregnancy, but it's thought to lower your risk of some cancers, including ovarian, endometrial and colorectal cancer.

While the breast cancer risk remains relatively low, women in their 40s or women genetically predisposed toward breast cancer may want to discuss other options for birth control with their doctor. These may include condoms or copper (non-hormonal) IUDs, or even permanent contraception methods like tubal ligation (surgery to close the fallopian tubes, which connect the ovaries to the uterus) and male vasectomy (surgery to cut the vas deferens, the tubes that carry sperm).

The American College of Obstetricians and Gynecologists (ACOG) also notes that progestin-only hormonal birth control does warrant more research. Progestin is a man-made version of the hormone progesterone. To prevent pregnancy, it’s given by itself or in combination with the hormone estrogen. (Most people take the combination pills.) Studies on progestin-only pills tend to have inconsistent results.

Ultimately, if you're on hormonal birth control or thinking of starting, speak with your OBGYN to weigh the risks and advantages, especially if you're in your late 30s or older.