Addiction is defined as a "persistent compulsive use of a substance known by the user to be harmful." Most people associate addiction with drug or alcohol use, or an activity like gambling. But there's increasing evidence that people, especially teens and pre-teens, are developing computer-related addictions to the Internet and video games.
The concept of video game (sometimes called "gaming") addiction is heavily debated among medical and mental health professionals. In early 2007, the American Medical Association (AMA) gathered scientific information dating from 1985 through 2007 on video games and their effects. The purpose was to "review and summarize the research data on the possible emotional and behavioral effects, including addiction potential, of video games..." The AMA discovered that, though more research is needed, the behaviors associated with video game overuse are similar to those of "pathological gambling" or gambling addiction. 
The term "Internet Addiction" was first coined in the 1990s by researchers who observed people using the Internet so much that other areas of their lives suffered. The word "addiction" was used because of the similarities in dysfunction between those who overuse the Internet or video games and other, more readily acknowledged forms of addiction.
People who get caught up in Internet or video game overuse often neglect family, friends, and school. They develop dependence-like behaviors, becoming agitated, bored, or restless when they're not gaming. Students often neglect homework, resulting in a decline in grades. They sometimes lose touch with their friends, choosing instead to invest in the "relationships" they develop while gaming. The antisocial aspect of gaming addiction is most common among those who play "massive multiplayer online role-playing games" or MMORPGs. These online games enable players to talk to each other, and a kind of online community is developed. When taken too far, however, the online community becomes more important than real-life friends and family.
Video game addiction is controversial because not all gamers who exhibit addiction-like behavior display any kind of withdrawal symptoms. Some gamers can go for days or weeks without playing. Still, some experts claim that the uncontrolled overuse is indicative of an actual addiction, with or without withdrawal.
In 2005, the Entertainment Software Association conducted a study on gaming and found that approximately 35 percent of all gamers are under 18 years of age. Approximately 9 percent of all gamers play MMORPGs, which is the segment most likely to become addicted.
As evidence mounts for the existence of video game addiction, researchers have tried to determine who is most at risk for addiction. So far, evidence suggests that young people who are socially awkward, perhaps considered outcasts at school, and are unusually lonely are most susceptible to gaming addiction. Many of these young people feel they are in more control online than they are in real life. They can create characters and reinvent themselves. They are readily welcomed in the online gaming community; a sharp contrast to how they feel at home or at school.
A number of studies have estimated that 10 percent to 15 percent of gamers exhibit signs that meet the World Health Organization's criteria for addiction. Symptoms include a compulsion to engage in the activity, difficulty ceasing the activity voluntarily, and a domination of the activity in the user's life to the exclusion of nearly all other activities. Research has also found that addictive and dependence behaviors occur more often in people who began playing at a very young age.
Based on the existing scientific research, the American Medical Association made several recommendations to both the gaming and medical communities. Among them was a recommendation to the Centers for Disease Control and Prevention, the National Institutes of Health, and similar organizations to fund research on the long-term effects of video game overuse. The AMA also recommended that the American Psychiatric Association review the report in preparation for the upcoming revision of the Diagnostic and Statistical Manual of Mental Health Disorders (DSM). The manual is due to be revised in 2012, and the AMA feels there is strong enough evidence to consider adding video game addiction as a diagnosable disorder.