A study led by the University of Delaware has found new evidence that being bullied in school may have lasting health consequences.

Using observational data collected from a sample of children who were studied over several years, researchers reported that kids who were bullied more frequently when they were younger were more likely to use certain drugs by the time they were in high school.

The study, which was published last week in the journal Pediatrics, adds to existing research finding a link between nasty treatment by peers and drug use.

The data came from more than 4,000 students sampled from districts in Los Angeles County, Birmingham, Alabama, and Houston, Texas, who were studied as they advanced from fifth to 10th grade. Among this racially and ethnically diverse group of students, suffering frequent incidents of "peer victimization" — used to measure how much a student had been bullied — in fifth grade was associated with using alcohol, marijuana, and tobacco in 10th grade.

Studying the same group of kids over time gave the researchers more confidence that bullying may have led to substance use by victims later on, said lead study author Valerie Earnshaw.

Researchers also looked at other data on students' emotional well-being that provides new insight into the connection, Earnshaw said. Victims of bullying in fifth grade were more likely to report depressive symptoms by seventh grade, the study found.

"So, depressive symptoms appear to link the peer victimization with the substance use," said Earnshaw, a professor at the University of Delaware.

Earnshaw said that finding suggests that some teens who were bullied a lot when they were younger may be using drugs to cope with its effects, even years later.

She said the results of the study lend hard evidence to the belief of many parents and teachers that bullying shouldn't be brushed off as a normal part of growing up, but considered a hazard to kids' health.

"I think it's important that we take these experiences seriously, and that we try to support youth who are experiencing bullying, and also try to end bullying when it is occurring," Earnshaw said.