A new study finds children who take stimulants to treat attention-deficit hyperactivity disorder (ADHD) are more likely to be bullied at school than their peers who do not have attention disorders. Those who have ever shared their prescriptions are at highest risk of bullying, Time reports.

Children who had shared their medication or had it taken from them in the previous year were four-and-a-half times more likely to be frequently bullied. The findings come from a survey of almost 5,000 children in five public schools.

“We know that among adolescents in the U.S., prescription stimulants are some of the most misused and shared diverted and drugs,” said lead researcher Quyen Epstein-Ngo of the University of Michigan. “We also know that bullying is a real issue. There was some research that suggested that kids were having their medication stolen or were being coerced into giving it away.”

The prevalence of children ages 4 to 17 who take ADHD medication increased from 4.8 percent in 2007 to 6.1 percent in 2011, according to the Centers for Disease Control and Prevention. Approximately 11 percent of children in this age group (6.4 million) were diagnosed with ADHD as of 2011.

Previous research suggests children with ADHD often have a more difficult time making friends, and are more likely to have anxiety and substance use disorders, the article notes. These conditions may increase the risk of bullying. Having stimulant medications in their possession increases the risk even more, Epstein-Ngo said.

“For some children stimulant medications are immensely helpful in getting through school,” Epstein-Ngo noted in a news release. “This study doesn’t say ‘don’t give your child medication.’ It suggests that it’s really important to talk to your children about who they tell.”

The study appears in the Journal of Pediatric Psychology.