Additional Study Information: The UPA Breast Study will investigate a medication called ulipristal acetate (UPA), which is currently used as an emergency contraceptive and as a treatment for fibroids. The study is designed to investigate 1) whether taking UPA daily can decrease breast cell proliferation compared to traditional combined oral contraceptive pills; and 2) whether MRI can replace biopsies in future research studies investigating breast proliferation, as substituting biopsies for MRI would make future studies easier for women to take part in. Study participation will last 4-5 months. The first month will consist of up to seven short study visits and end with a breast MRI and biopsy of one breast. The participant will then take UPA for three months. The participant will attend 12 visits during that time, culminating in a follow up Breast MRI and biopsy of the other breast. A brief study discontinuation visit will occur two weeks later.