Little is known about the comorbidity of Internet Use Disorder. There are reports of high comorbidity with mood disorders, especially depressive disorders, social phobia, attention deficit hyperactivity disorder (ADHD) and substance use disorder, but most of these studies have several methodological limitations.
In one of the first studies on the psychiatric comorbidity of compulsive computer use, Black et al. evaluated 21 individuals (16 men, 5, women) with self-reported excessive computer use. According to Black, of these 21 subjects 7 (33%) had a lifetime mood disorder, 8 (38%) a substance use disorder, 4 subjects (19%) had a lifetime anxiety disorder, and 11 subjects (52%) met criteria for at least one personality disorder (cf. Black 1999).
Shapira et al. evaluated 20 individuals with problematic internet use. All subjects met DSM-IV criteria for an impulse control disorder not otherwise specified (ICD-NOS) and all subjects had at least one lifetime DSM-IV Axis I diagnosis in addition to their problematic internet use (cf. Shapira 2000).
Kratzer et al. compared 30 individuals with pathological internet use and 31 individuals with intensive but non-pathological internet use. Among the patients with pathological internet use 90% showed symptoms of psychiatric disorders, especially anxiety disorders and mood disorders (cf. Kratzer 2008).
In a larger-scale survey Yen et al. evaluated 2114 Taiwanese students. Adolescents with symptoms of Internet addiction reported more symptoms of attention-deficit/hyperactivity disorder (ADHD), depression, social phobia, and hostility than adolescent without symptoms of Internet addiction (cf. Yen 2007). In the 2-year follow-up depressive disorders, social phobia, and hostility were found to predict the occurrence of Internet addiction (cf. Ko 2009).