Teenagers who frequently use smartphones and other digital devices are at a higher risk of developing attention-deficit/hyperactivity disorder (ADHD), a study has found.

ADHD is a brain disorder with symptoms that include a pattern of inattention, hyperactive behaviour and impulsiveness that interferes with functioning or development.

The study, published in the Journal of the American Medical Association, focuses on the mental health consequences of a new generation of ubiquitous digital diversions, including social media, streaming video, text messaging, music downloads and online chatrooms, among others.

"What is new is that previous studies on this topic were done many years ago, when social media, mobile phones, tablets and mobile apps didn't exist," said Adam Leventhal, a professor at University of Southern California in the US.

"New, mobile technologies can provide fast, high-intensity stimulation accessible all day, which has increased digital media exposure far beyond what's been studied before," Leventhal said.

The findings have ramifications for parents, schools, technology companies and pediatricians concerned that tech-dependent teens are driven to distraction or worse.

Scientists began with 4,100 eligible students, ages 15 and 16 years, across 10 public highs schools in Los Angeles County. They focused on teens because adolescence marks a moment for ADHD onset and unfettered access to digital media, Leventhal explained.

They pared to 2,587 participants by removing students for preexisting ADHD symptoms. The scientists' goal was to start with a clean slate to focus on occurrence of new symptoms manifest over the two-year study.

The researchers asked students how frequently they used 14 popular digital media platforms. They sorted media use frequency into three categories: no use; medium use and high use.

Scientists monitored the students every six months between 2014 and 2016. They sought to determine if digital media use in 10th grade was associated with ADHD symptoms tracked through 12th grade.

In the end, they found 9.5 per cent of the 114 children who used half the digital media platforms frequently and 10.5 per cent of the 51 kids who used all 14 platforms frequently showed new ADHD symptoms.

By contrast, 4.6 per cent of the 495 students who were not frequent users of any digital activity showed ADHD symptoms, approximate to background rates of the disorder in the general population.

"We can't confirm causation from the study, but this was a statistically significant association," Leventhal said.

"We can say with confidence that teens who were exposed to higher levels of digital media were significantly more likely to develop ADHD symptoms in the future," he said.

The findings help fill a gap in understanding how new, mobile media devices and seemingly limitless content options pose a mental health risk to children. It serves as a warning as digital media becomes more prevalent, faster and stimulating.

"This study raises concern whether the proliferation of high-performance digital media technologies may be putting a new generation of youth at risk for ADHD," Leventhal said.