Adopted children are far more likely to have troubled adolescences than are kids who live with their biological parents, says a new study. Minnesota researchers evaluated the mental health of more than 1,200 adopted and non-adopted children and found that the adopted children were twice as likely to suffer from such conditions as ADHD and oppositional defiant disorders. “All adolescents struggle with finding their identity,” study author Margaret Keyes tells Time. “It makes sense that adopted children would struggle more than most.” But Keyes stresses that it’s possible that adopted youngsters’ problems have just as much to do with their biological parents as with the challenges of being raised in an adoptive family. She notes, for instance, that a genetic predisposition to mental-health difficulties may be more common among people who give up their babies for adoption.