She teaches History, Medicine, Gender and Women's Studies, and Law, specializing in the history of medicine, U.S. women's history, the history of sexuality, and 20th century U.S. social history. Her book, When Abortion was a Crime: Women, Medicine, and Law in the United States, 1867-1973 (University of California Press, 1996), earned multiple awards and has been the basis of many presentations, lectures and international media interviews. Professor Reagan joined the Illinois History faculty in 1992, and is a member of the Medical Humanities and Social Sciences Program in the College of Medicine. Her current research focuses on the history of illegal abortion, the intersections between law and medicine, and social and legal issues relating to breast cancer and public health.