A new study finds 13 percent of high school seniors have used prescription opioids for non-medical reasons. Overall, nearly one in every four high school seniors in the United States has had some exposure to prescription painkillers, either for medical or non-medical reasons.

The study of 7,374 high school seniors by researchers at the University of Michigan found about 80 percent of teens who used prescription opioids for non-medical reasons after having initially used the drugs for medical purposes, had obtained the drugs from an old prescription.

Teens who used painkillers for non-medical reasons were more likely to smoke marijuana or cigarettes, or to binge drink, compared with teens who had only taken painkillers under a doctor’s supervision, or did not take the drugs at all, Reuters reports.

The study appears in the journal Archives of Pediatrics and Adolescent Medicine.

The recently released 23rd annual Partnership Attitude Tracking Study found that teen lifetime abuse of medicines is plateauing and holding steady at 17 percent for prescription drugs, and 12 percent for over-the-counter cough and cold medicines. Among teens, past year abuse of the prescription pain relievers Vicodin and OxyContin has plateaued at about 10 percent, the study found.