Eligible women will present to the division research office, at which time a history and physical exam will be completed. Each participant's BMI will be confirmed and she will be assigned to one of two BMI groups (18.5-24.9 versus 30-39.9). At the conclusion of the enrollment visit, the research coordinator will randomize each woman to receive a single-dose pill of either levonorgestrel 1.5mg (like Plan B One-Step® or its generic formulations) or ulipristal acetate 30mg (ellaOne®) on two separate occasions.