The study, published on the British Medical Journal website, found that many adolescents are loathe to seek help for mental health issues.
To tackle that problem, researchers developed an interactive fantasy game called Sparx which sees each player choose an avatar and then face challenges to restore balance in a virtual world overrun by Gnats (Gloomy Negative Automatic Thoughts).
They found the self-help game, which uses cognitive behavioural therapy techniques to help young users, had as much benefit as more traditional treatments, reducing symptoms of depression and anxiety by at least one-third.
Of the 187 young people in New Zealand studied as part of the trial, significantly more recovered completely in the group playing the computer game.
A total of 44% of those who completed at least four of the seven modules in Sparx recovered, compared to 26% of those who were receiving face-to-face treatment.
In the Sparx group, 95% of the adolescents said they felt the game would appeal to other teenagers and 81% would recommend it to a friend.