Introduction: The American Psychiatric Association included Internet gaming disorder (IGD) in the 5th Edition of the Diagnostic and Statistical Manual of Mental Disorders, and the World Health Organization included gaming disorder in the 11th revision of the International Classification of Diseases. These recent updates suggest significant concern related to the harms of excessive gaming. Areas covered: This systematic review provides an updated summary of the scientific literature on treatments for IGD. Inclusion criteria were that studies: 1) evaluate the effectiveness of an intervention for IGD or excessive gaming; 2) use an experimental design (i.e. multi-armed [randomized or nonrandomized] or pretest-posttest); 3) include at least 10 participants per group; and 4) include an outcome measure of IGD symptoms or gaming duration. The review identified 22 studies evaluating treatments for IGD: 8 evaluating medication, 7 evaluating cognitive behavioral psychotherapy, and 7 evaluating other interventions and psychosocial treatments. Expert opinion: Even with the recent uptick in publication of such clinical trials, methodological flaws prevent strong conclusions about the efficacy of any treatment for IGD. Additional well-designed clinical trials using common metrics for assessing IGD symptoms are needed to advance the field.

The thesis concerns factors that affect the intensity of MMORPG playing and the gaming addiction symptoms. In the theoretical part, I discuss approaches to the excessive and problematic gaming. I argue for the shift of perspective from gaming addiction disorder toward self-regulation, time perspective, activity theory and habitual regulation. Two inventory-based studies were conducted in order to empirically verify the effect of proposed variables on MMORPG usage. First, the significant role of Time Perspective (TP), measured by Zimbardo Time Perspective Inventory (ZTPI), has been confirmed. Second, the habitual regulation had been identified to significantly affect the usage. The habits related to usage were measured by the new psychometrical tool - Cues Sensitivity Scale (CSS). TP and habits influence the usage together - the effect of TP is partially mediated through Cues Sensitivity as well as through the players' deliberate regulation of playing time. All measured variables showed stability in time (measured after three years in subset of respondents). Data was analyzed with statistical methods, mainly with Partial-Least-Squares Path- Modelling (PLS-PM). The part of the data - respondents' strategies of playing time regulation - were analyzed qualitatively.