A new study at Columbia University Mailman School of Public Health suggests there is a two-way relationship between bullying perpetration and mental health problems among youth in the U.S. Researchers report that bullying perpetration increased the risk of developing internalizing problems, and having internalizing problems increased the probability of bullying others. While previous research has focused on the causes and consequences of bullying victimization, this is the first study to comprehensively explore the time sequence between bullying perpetration and mental health problems. The results are published online in the Journal of Adolescent Health. More information.