The study, carried out by Dr Brady and Professor Karen Matthews at the University of Pittsburgh, involved a group of 100 male undergraduates aged 18 to 21, asked to play either Grand Theft Auto III or The Simpsons: Hit and Run. In GTA the player took the role of a criminal and was instructed by the Mafia to beat up a drug dealer with a baseball bat. In The Simpsons: Hit and Run the player took on the role of Homer Simpson attempting to get his daughter's science project to school before it can be marked late.

The study claims that the men who have just played a violent game (GTA) are more likely to see others' attitudes towards them as hostile, smoke marijuana, and drink alcohol.

"Parents have been told the message that violent video games and violent media in general can influence the likelihood that their kids will be aggressive," Dr. Sonya S. Brady told Reuters Health. "What this study suggests is that they might increase any type of risk-taking behaviour."

According to the report in the Archives of Pediatrics and Adolescent Medicine, playing a violent game caused young men's blood pressure to increase, and appeared to have a greater effect on those that came from violent homes or communities. No matter what background each male had, the researchers found that playing a violent game made the young men in the study less cooperative and more competitive in completing tasks with another person.

After playing one of the games, the males participating in the study were shown a scenario of a teacher telling his class that he suspects some students have cheated, but also that he is proud of those who did well. The teacher then asks a boy called Billy to stay behind after class so that he may speak with him. Participants were then asked to put themselves in Billy's position. When asked how likely it was that the teacher was going to accuse them of cheating, those participants who had been playing Grand Theft Auto were more likely think they would be accused.

The report is also one of the first to link violent games to behaviour other than violence, but will no doubt provide more ammunition to those against violent video games.