Problematic internet use (PIU) is a growing behavioral health concern among university students. This study aims to evaluate the effectiveness and psychological mechanisms of "IMPROVE," a manualized, multimodal group-based psychotherapy. The IMPROVE program integrates cognitive-behavioral strategies with motivational elements, mindfulness training, and socially interactive exercise. In this randomized controlled trial, 600 university students with moderate to severe PIU will be randomized to either the 8-week IMPROVE intervention or an enhanced waitlist control group. The primary outcome is the change in PIU severity, assessed by the Internet Addiction Test (IAT) score, from baseline to the post-intervention endpoint (8 weeks).

Problematic internet use (PIU) has emerged as a prevalent and clinically significant behavioral health problem among university students, characterized by impaired control over online behaviors and associated psychological distress, functional impairment, and academic difficulties. It is increasingly conceptualized as a spectrum of heterogeneous behaviors (e.g., gaming, social media use, short-form video consumption) rather than a single homogeneous entity.

Although a growing body of research has examined interventions for PIU, the current evidence base remains limited by several methodological shortcomings, including small sample sizes , short intervention durations, insufficient follow-up, insufficient consideration of the heterogeneity of PIU, and a lack of theory-driven investigation into psychological mechanisms of change. Moreover, many existing interventions focus on single components (e.g., cognitive-behavioral techniques alone), while neglecting the multidimensional nature of PIU, which involves complex interactions between cognitive biases, emotion dysregulation, and anhedonia.

To address these gaps, this prospective, single-blind, parallel-group randomized controlled trial evaluates the efficacy, durability, and potential mechanisms of action of a manualized, group-based intervention-IMPROVE therapy-for treatment-seeking university students with PIU. IMPROVE therapy is designed as an integrative program that combines cognitive-behavioral strategies with motivational elements, mindfulness training, and socially interactive exercise, targeting core psychological processes implicated in the development and maintenance of PIU.

Eligible participants will be randomized in a 1:1 ratio to receive immediate IMPROVE therapy or an enhanced waitlist control. Crucially, randomization will be stratified by the sex, age, severity of PIU and primary PIU subtype (e.g., gaming, social media, short-form video) to ensure balanced allocation and facilitate potential subgroup analyses. Participants in the IMPROVE group receive an 8-week structured group therapy consisting of one 120-minute session per week . Outcome assessments are conducted at baseline (T0), mid-intervention (Week 4, T1), post-intervention (Week 8, T2), and at follow-up time points of 1 month (T3), 3 months (T4), 6 months (T5), and 12 months (T6) after completion of the intervention.

The primary objective of the trial is to determine whether IMPROVE therapy leads to a greater reduction in PIU severity compared with the enhanced waitlist control at the end of the intervention. Accordingly, the primary outcome is PIU severity measured by the Internet Addiction Test (IAT), operationalized as the between-group difference in change in IAT total score from baseline (T0) to the post-intervention endpoint (T2).

The secondary objectives are to evaluate (1) the maintenance and durability of treatment effects across short-, medium-, and long-term follow-up periods, and (2) additional clinically relevant outcomes related to PIU. Secondary outcomes therefore include IAT scores at follow-up time points (T3-T6), rates of clinical remission defined by a prespecified IAT threshold, changes in associated psychological symptoms and functional impairment, and indicators of feasibility, adherence, and acceptability of the group-based intervention.

A core objective of this trial is to elucidate how the intervention exerts its effects. Guided by the I-PACE model, the study assesses potential mediators at Baseline (T0), Mid-intervention (T1), and Post-intervention (T2). Longitudinal mediation analyses will test whether improvements in Maladaptive Cognitions, Emotion Regulation, Self-Efficacy, Anhedonia, Perceived Stress, Mind Wandering, Resilience precede and mediate reductions in PIU severity.

A subset of participants will voluntarily undergo neuroimaging (fMRI) and blood sampling at T0 and T2 to explore the neurobiological correlates of therapeutic change.

Outcome assessors and data analysts will be blinded to treatment allocation to minimize assessment and analytic bias.

Inclusion Criteria:

• University students aged between 18 and 30 years.
• Score 50 or above on the Internet Addiction Test (IAT), indicating moderate to severe PIU.
• Report subjective suffering regarding internet use.
• Own a personal smartphone or other electronic communication device.
• Provide written informed consent

Exclusion Criteria:

• Self-reported history of substance use (excluding tobacco and alcohol) within the past 12 months.
• Current or previous participation in any form of psychotherapy for PIU.
• Presence of severe physical or neurological conditions (e.g., organic brain diseases, TBI).
• Self-reported history of diagnosed psychiatric disorders (e.g., schizophrenia, bipolar disorder).

Participants and therapists cannot be blinded due to the nature of psychotherapy. Outcome assessors and data analysts will remain blinded.