The negative effects of the Internet and social media on young people could be far greater than previously thought, suggests new research.
Scientists have found a link between excessive use and mental health problems.
University-aged students addicted to scrolling social media sites, watching videos online and browsing web pages are more likely to suffer from depression, anxiety, impulsiveness, inattention, executive functioning or ADHD.
The shocking revelation proves fears that increasing numbers people are becoming unable to cope without regularly going online.
Researchers at McMaster University in Canada surveyed 254 students using the Internet Addiction Test (IAT), created in 1998, as well as a newer scale of their own design.
Chief researcher Professor Michael Van Ameringen said: "We found that those screening positive on the IAT as well as on our scale, had significantly more trouble dealing with their day- to-day activities, including life at home, at work, school and in social settings."
The study found that 33 of the students surveyed met screening criteria for internet addiction according to the IAT.
University students showed the most difficulty controlling their use of video streaming sites, with 55.8 per cent struggling, 47.9 per cent couldn't control their social media use and 28.5 per cent had difficulty staying away from instant messaging tools.
However, three times as many students met criteria for problematic internet use using Professor Van Ameringen and colleagues' new screening tool - 107 flagged up in the test - which is more likely to reflect modern internet use.
Professor Van Ameringen said: "The IAT was developed in 1998, prior to the widespread use of smartphone technology.
"In addition, internet use has changed radically over the last 18 years, through more people working online, media streaming, social media, etc.
"We were concerned that the IAT questionnaire may not have been picking up on problematic modern internet use, or showing up false positives for people who were simply using the internet rather than being over-reliant on it."
With 42.1 per cent of those surveyed facing mental health problems as a result of excessive Internet use, scientists are now questioning if the prevalence of internet addiction is grossly underestimated and if additional mental health issues are a cause or consequence of the excessive reliance on the Internet.
Commenting on the findings, Professor Jan Buitelaar, of Radboud University Nijmegen Medical Centre and the ECNP child and adolescent disorders treatment Scientific Advisory Panel, said: "Excessive use of the internet is an understudied phenomenon that may disguise mild or severe psychopathology.
"Excessive use of the internet may be strongly linked to compulsive behaviour and addiction; as the authors say, further study is needed in larger populations."
Professor Van Ameringen believes the findings may have practical medical implications.
He added: "If you are trying to treat someone for an addiction when in fact they are anxious or depressed, then you may be going down the wrong route.
"We need to understand this more, so we need a bigger sample, drawn from a wider, more varied population."
The findings will be presented at the 29th annual European College of Neuropsychopharmacology Congress in Vienna.