Nationwide study finds higher rates of breast cancer with current or former use of oral contraceptives.

Women who use hormonal birth control have a higher risk of breast cancer, according to a study of nearly 1.8 million women in Denmark.

Past efforts to evaluate a link between breast-cancer risk and hormonal contraception yielded conflicting results, and often focused on older formulations of the drugs. To learn about the risk of modern birth control, Lina Mørch and Øjvind Lidegaard at the University of Copenhagen and their colleagues analysed data collected from 1995 to 2012, and adjusted for factors such as age and family history of breast cancer.

They found that the risk of breast cancer was 20% higher in current and recent users of hormonal contraception than in those who had never used the drugs. Risk was lower when birth control was used for less than one year, compared with longer use.

Overall, the data suggested that hormonal contraceptives are linked to one additional case of breast cancer for every 7,690 women using the drugs for one year.