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Birth Control May Raise the Risk of Breast Cancer

Birth Control May Raise the Risk of Breast Cancer
From TIME - December 6, 2017

Doctors should be having more detailed discussions with women before prescribing them birth control, say researchers who have been studying the risks and benefits of hormone-based contraceptives.

In a new study published in the New England Journal of Medicine, Ojvind Lidegaard from the University of Copenhagen and his colleagues found a 20% higher risk of developing breast cancer among women currently or recently using hormonal contraceptives. The longer women used contraceptives, the higher their risk; it increased from about 9% for women using it for less than a year to 38% for those using them for 10 years or more.

The study was based on a unique health registry in Denmark, where all filled prescriptions are required to be recorded by law. The prescription information was matched with a cancer registry to document any associations between contraceptives and breast cancer. Lidegaard and his team tracked all hormonal contraceptives, which include oral birth control pills, patches, vaginal rings, hormone-releasing IUDs, injections and the so-called morning after emergency birth control. The highest associated risk occurred with users of the emergency birth control levonorgestrel, or Plan B, compared to women not using contraception.

Ledegaard points out that the increasing breast cancer risk associated with longer use of hormonal contraceptives strongly suggests a connection between the contraceptives and cancer. The fact that we can demonstrate such a linear effect to the length of use makes a causal inference more likely, he says.

MORE: A Brief History of Birth Control

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