Since the 1990s, uncontrolled or unreasonable Internet use has been identified as a problem with signs similar to other addictions, researchers say.
Pathological Internet use has been linked with relationship problems, health problems, aggressive behavior and other psychiatric symptoms, they added.
"Parents should be vigilant about their children's online behavior," said lead researcher Lawrence T. Lam, from the School of Medicine, Sydney, and the University of Notre Dame Australia.
"Should there be any concern about young people involving problematic Internet-use behavior, professional help should be sought immediately. "This sort of behavior may be a manifestation of some underlying problems that are more insidious, Lam said.
"Given the results obtained from the study, even mentally healthy young people may succumb to depression after a long exposure of problematic use of the Internet.
The mental health consequences of problematic Internet use for those who have already had a history of psychological or psychiatric problems would be more damaging," he said.
At the start of the study, the researchers classified 6.2 percent
of the teens as having a moderately pathological Internet problem and 0.2 percent as seriously at risk.
Nine months later, the teens were reassessed for depression and anxiety. The researchers found 0.2 percent had symptoms of anxiety and 8.4 percent had become depressed.
The risk of becoming depressed was 2.5 times higher among teens who were addicted to the Internet compared with those who werenot, Lam and Peng found.
However, there was no association between pathological Internet use and anxiety, they noted. "This study has a direct implication on the prevention of mental illness among young people," Lam said.
"The results of the study indicated that young people who use the Internet pathologically are most at risk of mental problems and would develop depression when they continue with that behavior."
Early intervention and prevention that targets at-risk groups with identified risk factors is effective in reducing the burden of depression among young people, Lam added.
"Screening for at-risk individuals in the school setting couldbe considered as an effective early prevention strategy," he said.
"Hence, a screening program for pathological use of the Internet could also be considered in all high schools in order to identify at-risk individuals for early counseling and treatment."
"Parents are indicating to us that a lot of their children's friendship circles are contracting by reason of the fact they are spending too much time on the Internet," he said. "This ties in generally with the notion that Internet behavior is becoming disruptive in the family."
Spending too much time on the Internet is a so-called "process addiction," like gambling and pornography, Gilbert said.
"We are going to see more of these problems, and 'they' are especially acute in adolescence when kids are struggling with defining their social circumstances," he said.
"The technology changes, the medium changes, but the issue always comes down to parents ascertaining control over their children's behavior and monitoring it," he said.
