Internet-based Versus Synchronous Cognitive Behavioural Therapy for Patients With Gambling Disorder

The aim of this two-armed, randomized controlled trial is to determine if internet-based cognitive behavioural therapy (CBT) is as effective as synchronous CBT (sCBT) for treating Gambling Disorder (GD) in adults. The main question it aims to answer is: Is the effect of the internet-based CBT ("SpilleFri") non-inferior to that of synchronous CBT in reducing gambling severity? The trial will enroll 150 patients with Gambling Disorder who will be randomized (1:1) to either the experimental condition (12 weeks' treatment with the internet-based treatment "SpilleFri") or the active control condition (18 weeks individual sCBT). The primary outcome measure will be based on self-reported GD severity (NODS). The trial will be considered effective if SpilleFri is not clinically inferior (within a predefined non-inferiority margin) to sCBT in reducing GD severity at the primary endpoint three months after end-of-treatment. In addition to evaluating the effectiveness of the treatments, the study will conduct an exploratory analysis of the impact of each condition on secondary outcomes (changes in gambling behavior, relationship quality, and symptoms of anxiety, depression, and emotional distress). Similarly, an exploratory analysis of process variables (gambling-related self-efficacy, maladaptive gambling cognitions, emotion regulation difficulties, and gambling urge) will be conducted across conditions and clinical subgroups. Participants will: * Engage in nine structured modules of either internet-based CBT or sCBT * Complete self-reported questionnaires on gambling severity and secondary symptoms at eight time points * Have the option for up to three additional support sessions with a psychologist