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

PROJECT GROUP: Anna Westh Stenbro (Psychologist, MSc.); Lisbeth Frostholm (Professor, Psychologist, MSc., Ph.D.); David Hodgins (Professor, Psychologist, MSc., Ph.D.)

The trial will be conducted by the research group at the Research Clinic for Gambling Disorder, based at Aarhus University Hospital, Denmark. The clinic was established in 2007 and offers assessment and specialized treatment to patients with GD.

MEASUREMENTS:

Self-reported data from the participants are collected at seven time points: At baseline (T1), randomisation (T2), three time points mid-treatment (T3, T4, T5), end-of-treatment (T6) and at 3-month follow-up (T7, primary endpoint). Due to different treatment durations in the two arms, an additional measurement point (T7b) is added to control for the effect of time for participants in the SF group, at the time point when participants in the sCBT group complete the 3-month follow-up (week 30). At T6, all participants will be invited to participate in a 12-month follow-up study (T8).

During treatment, therapists register the length, and themes, of phone conversations and face-to-face sessions in SpilleFri and equally the length and overall themes of sessions in the sCBT arm. In both arms, therapists register involvement of concerned significant others in treatment sessions. In the sCBT arm, therapist register manual fidelity and covered intervention topics after each session. Deviations are described. At the end of the treatment course, the therapists evaluate participant engagement and treatment effect (CGI-I).

For a detailed list of the measures and measurement time points included, see the section "Outcome measures".

RANDOMIZATION:

Included patients will be randomized to SF or sCBT in a 1:1 ratio. Randomization takes place immediately following the inclusion conference. A member of the research group will perform the randomization using the randomization module in the online data collection program, REDCap. When the randomization module is activated, REDCap automatically and randomly assigns participants to one of the predefined study groups in randomization blocks randomly ranging between 8 and 12. All research group members and clinicians are blinded to the current randomization block size.

POWER CALCULATION:

Sample size estimation was done using simulation of mixed linear models in Stata version 17. The relative effects of SF and sCBT will be analysed using a pre-set non-inferiority margin, determining the margin within which SF can be less effective than sCBT without being declared clinically inferior to the standard treatment. Within this margin, any difference in effect will represent a clinically unimportant loss of effect.

Simulation parameters were informed by 1) previous clinical data from the RCGD on reduction in NODS for patients given sCBT and 2) reduction in NODS for patients in the SF feasibility study. Assuming baseline-EOT-FU trajectory in NODS-score of 7-1-1 in individual CBT condition and 7-2-2 in SF condition, power of .80 was reached for 100 patients (50 in each condition). To account for dropout and attrition, a sample size of 150 is ideal.

ANALYSIS:

The hypothesized non-inferiority of SF compared to individual CBT as measured by NODS will be analysed using 2-level mixed linear models with random intercept - i.e., repeated measures nested within patients. REML estimation will be employed. Model-predicted mean change in NODS from baseline to FU is estimated in both CBT and SF condition, and a 95% confidence interval for the difference in change, i.e., ΔCBT-ΔSF, is calculated. The null-hypothesis of inferiority is rejected if the upper bound of this confidence interval is greater than the inferiority bound defined to be -2 NODS-scale points, i.e., SF leads to a change in NODS not more than 2 points less than CBT. The inferiority bound was decided based on clinical experience from RCGD, judging how large a difference in NODS that is clinically visible.

Results will be analysed and reported according to the CONSORT statement. A statistician is continuously involved in the project.

Inclusion Criteria:

To be included patients should:

• fulfil diagnostic criteria for GD (DSM-5).
• score 4 points or more on the National Opinion Research Centre Screen for Gambling Problems (NODS).
• be able to read, write, and speak Danish.
• have IT skills and access to the internet and a computer, smartphone, and/or tablet.

Exclusion Criteria:

Patients are excluded from participation if they:

• present with severe comorbid somatic disease, cognitive deficits, severe trauma, and/or psychiatric disorder (e.g. depression, bipolar disorder, substance abuse, ADHD) that is insufficiently treated at the time of assessment and/or is evaluated to constitute a barrier for engaging in or benefitting from treatment.
• are not willing to engage in internet-delivered treatment or face-to-face cognitive behavioural therapy.
• do not provide informed consent.
• are in risk of suicide (indicated by clear intent and/or plans).
• have previously received treatment via or had access to the SpilleFri platform.
• seek treatment as part of an imminent legal case.
• only fulfil diagnostic criteria for Gambling Disorder in relation to behaviour such as stock trading or buying and selling cryptocurrency.
• present with highly unstable social circumstances, which are considered to potentially pose a barrier to engaging in treatment (e.g., homelessness).

To protect participant anonymity, individual participant data (IPD) will not be shared. Instead, aggregate data will be shared in an anonymized form.