This RCT study develops a brief group-based CBT intervention. The primary objective is to evaluate the efficacy of the CBT in reducing IGD, compare to a wait-list control group.

Introduction Cognitive behavioral therapy (CBT) is potentially useful as it is effective in treating mental/behavioral disorders, restructuring cognitions and cultivating positive coping. A gap exists as the only two existing clinic-based small randomized controlled trials (RCT) yielded mixed findings on CBT's treatment effect for adolescent IGD.

Objectives This RCT study develops a brief group-based CBT intervention. The primary objective is to evaluate the efficacy of the CBT in reducing IGD, compare to a wait-list control group.

Subjects and methods The study design is two-armed RCT. The participants are Secondary 1-4 students (n=226) with IGD (DSM-5 classification) identified in a school-based screening. Evaluation involves surveys at baseline, end of CBT intervention, and 6 months afterwards. In addition to information received by the wait-list control group, the intervention group receives a carefully designed brief 8-week group-based CBT. The control group will receive CBT after the 6-month follow-up. Trained social workers of a collaborating NGO that serves secondary school students will conduct the CBT.

Outcomes and measures The primary outcome is IGD (a validated DSM-5 IGD classification tool). Secondary outcomes include time spent on Internet/Internet games and the intention to reduce IGD. Measures of potential mediators (maladaptive beliefs and coping) include: Internet Gaming Cognition Scale, Generalized Problematic Internet Use Scale, Emotion Regulation Questionnaire, and Coping Scale for Children and Youth.

Data analysis Intention-to-treat analysis is performed. The primary outcome is assessed by absolute and relative risk reduction. Generalized Linear Mixed Models and Structural Equation Models are used to test secondary outcomes and mediation effects.

Implications The findings may lead to an evidence-based treatment for adolescent IGD, a newly defined disease, which has been rarely reported in literature. Understanding its mechanism contributes to theoretical development of IGD and related treatment.

Inclusion Criteria:

• secondary 1-4 students (grade 7-10),
• positive screening results (i.e. IGD cases) according to a validated questionnaire (the 5 DSM-5 criteria for IGD),
• students' and parental consent,
• Chinese speaking.

Exclusion Criteria:

• self-reported history of any psychiatric or neurological illness,
• current use of any psychotropic medication.

We do not include Secondary 5-6 students due to their preparation for public examinations and practical difficulty in follow-up after their graduation.