<p>Assumed components explaining the change of symptom severity in problematic usage of the internet are general predisposing factors including psychopathology (e.g., compulsivity, depression, anxiety, chronic stress) and behavior-specific factors (e.g., use expectancies, experience of gratification/compensation, usage time, habitual use). We screened for symptom severity based on ICD-11 and DSM-5 criteria and assessed all mentioned factors at baseline and in a 6-month follow-up (<i>N</i> = 574). Change scores of the predictors and whether participants received therapy explained about 20% of variance in symptom change scores; <i>R</i>² = .199 for ICD-11 and <i>R</i>^<i>2</i> = .216 for DSM-5 criteria. Strongest predictors of symptom change were as follows: received therapy, avoidant use expectancies, time of use, habitual use, depression, compulsivity, and chronic stress. Results indicate that a decrease of symptom severity is related to decreased levels of variables associated with negative reinforcement mechanisms. Treatment, even if not addiction-specific, proved to be beneficial. The influence of external factors warrants further research.</p>