Millions of Women Take This Daily Medication. It’s Now ‘Confirmed’ to Increase Breast Cancer Risk

A massive study of more than 2 million women has “confirmed that increased risk of breast cancer was associated with hormonal contraceptive use” — but researchers warn that the benefits of the pill may still outweigh the risk.

Researchers found that women who took birth control that contains only one hormone, a form of progesterone called desogestrel, were at a 21% increased risk of developing breast cancer, whereas those on combination pills had a 12% higher risk. “The finding that desogestrel may increase breast cancer risk more than other progestins is a novel finding that, to our knowledge, has not been previously reported,” said the study, published in JAMA Oncology.

Given that the combination pills presented a lower risk of breast cancer, researchers wrote, “These results also suggest that estrogen may attenuate progestin’s harmful effect.” 

The minipill, or a progestin-only pill, works by thickening cervical mucus (making it harder for sperm to travel into the uterus), stopping ovulation and thinning your uterine lining, preventing a fertilized egg from implanting, the Cleveland Clinic explains, whereas combination pills, which achieve the same effects, also contain estrogen.

The minipill comes in a pack with 28 “active” pills; the combination pills have three weeks of active pills and one week of inactive, or placebo, pills.

The researchers noted that, while further study is needed, the “statistically significant” risks “should be considered in the broader context of the well-established benefits” of taking hormonal contraceptives.

“These benefits include prevention of unintended pregnancies, which are associated with increased maternal morbidity and mortality, as well as their protective effects against ovarian and endometrial cancers,” the study reads. “Collectively, these considerations highlight the importance of personalized contraceptive counseling that takes into account individual risk profiles and preferences.”