The study led by Elisabeth F. Beaber, PhD, MPH, at Fred Hutchinson Cancer Research Center in Seattle, Wash. looked at the electronic pharmacy records of women who recently used birth control pills containing high-dose estrogen. They found that some of the formulations increased breast cancer risk 2.7 times, and those containing moderate-dose estrogen increased the risk 1.6-fold compared to women who did not use those contraceptives.
Pills containing ethynodiol diacetate (Kelnor, Zovia) increased the risk 2.6-fold, and extended-cycle and continuous-cycle combination pills containing an average of 0.75 milligrams of norethindrone (Aygestin®, Norlutate®, Norlutin®) increased the risk 3.1-fold. Birth control pills containing low-dose estrogen did not increase breast cancer risk.
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