The number of children diagnosed with ADHD has reached more than 10 percent, a significant increase during the past 20 years.
Findings could help improve treatments and reduce ADHD side effects.
They said the discovery could lead to new treatments for gambling addiction, through drugs or psychological techniques.
Researchers at McGill University looks into smartphone addiction and social interaction.
German researchers say they were unable to find any relevant negative effect.
The World Health Organization recognized a new condition: Gaming disorder.