The intervention group receives the login data for the online program directly following the baseline assessment. The program consists of 10 modules with many interactional exercises and homework-sheets.

Themes that are addressed in the online-program are for example self-esteem, sleep hygiene, problem solving strategies, mindfulness-based relaxation and attention exercises as well as gambling-specific topics such as money/debt management and impulse control. In addition, the user learns to modify negative and gambling-specific thought distortions, to integrate positive activities into his/her daily routine, strategies to deal with the urge to play as well as ways to regulate debts and to prevent relapse.

The participants of the wait-list control condition do not receive any new intervention during the intervention period of 8 weeks, but may continue any treatment that has already been started before, including medication. Participants in the wait-list control condition receive full access to the program after completion of the post-assessment.

The program consists of 10 modules with many interactional exercises and homework-sheets. Themes that are addressed in the online-program are for example self-esteem, sleep hygiene, problem solving strategies, mindfulness-based relaxation and attention exercises as well as gambling-specific topics such as money/debt management and impulse control. In addition, the user learns to modify negative and gambling-specific thought distortions, to integrate positive activities into his/her daily routine, strategies to deal with the urge to play as well as ways to regulate debts and to prevent relapse.

The total score consists of ten items that measure the severity of gambling symptoms within the past week. The first five questions assess urges and thoughts associated with gambling, whereas the last five questions assess the behavioral component of the disorder. The sum score of each subscale ranges from 0-20. Each subscale can be analyzed separately as well as together as a total score (primary outcome). The total score can be interpreted as follows: 0-7 sub-clinical, 8-15 mild, 16-23 moderate, 24-31 severe and 32-40 extreme gambling symptoms.

The Patient Health Questionnaire - 9 depression module is a self-rating measure of depressive symptom severity. The psychometric properties of the PHQ-9 are very good, with high internal consistency (Cronbach's α = .86 - .89; Kroenke, Spitzer, & Williams, 2001). Its sum score ranges from 0 to 27, with scores from 0-4 indicating minimal depression, 5-9 mild depression, 10-14 moderate depression and 15-27 severe depression.