Internet addiction is not recognized as a formal mental health disorder. However, mental health professionals who have written about the subject note symptoms or behaviors that, when present in sufficient numbers, may indicate problematic use. These include:
- Preoccupation with the Internet: User often thinks about the Internet while he or she is offline.
- Loss of control: Addicted users feel unable or unwilling to get up from the computer and walk away. They sit down to check e-mail or look up a bit of information, and end up staying online for hours.
- Inexplicable sadness or moodiness when not online: Dependency on any substance often causes mood-altering side effects when the addicted user is separated from the substance on which he or she depends.
- Distraction (Using the Internet as an anti-depressant): One common symptom of many Internet addicts is the compulsion to cheer one's self up by surfing the Web.
- Dishonesty in regard to Internet use: Addicts may end up lying to employers or family members about the amount of time they spend online, or find other ways to conceal the depth of their involvement with the Internet.
- Loss of boundaries or inhibitions: While this often pertains to romantic or sexual boundaries, such as sharing sexual fantasies online or participating in cyber sex, inhibitions can also be financial or social. Online gambling sites can cause addicts to blow more money than they would in a real-life casino because users never actually see their money won or lost, so it is easier to believe the money is not real. Chat rooms can incite users to reveal secrets they would not reveal in face-to-face or phone conversations because of the same separation from reality. Also, addicted users are much more likely to commit crimes while online (e.g., 'hacking') than non-addicts.
- Creation of virtual intimate relationships with other Internet users: Web-based relationships often cause those involved to spend excessive amounts of time online, attempting to make connections and date around the Net.
- Loss of a significant relationship due to Internet use: When users spend too much time on the Web, they often neglect their personal relationships. Over time, such relationships may fail as partners simply refuse to be treated badly and break off from relations with the addicted individual.