Elizabeth Renstrom for TIME
By Alice Park
December 6, 2017
TIME Health
For more, visit TIME Health.

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

The results come on the heels of another study Lidegaard and his team published in November, which found a correlation between hormonal contraceptives and an increased risk of suicide attempts and suicide. Previous studies have also linked oral contraceptives to a risk of breast cancer, as well as to blood clots.

Taken together, he says, it’s time to re-evaluate hormonal contraceptives and remind doctors that they should be discussing the risks and benefits of the drugs before prescribing them. Too often, he says, doctors don’t follow up on women taking them because overall, they are safe. He says that the absolute risk of mood disorders and cancer is still small, but enough to warrant deeper back and forth with women about their individual risk. Women with a history of mood disorders and depression, for example, or a family history of these conditions, should be evaluated more closely after being prescribed a hormonal contraceptive.

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The same should apply to women at higher risk of breast cancer because of a family history of the disease. Lidegaard uses a trial period when prescribing hormonal contraceptives, carefully evaluating women for about three months after they first start on the medications. “Women understand that whatever they do carries risk, and hormonal contraceptives are no exception,” he says. “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.”

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