This thesis investigates how problematic smartphone use (PSU) may explain the link between ADHD symptoms and problematic alcohol use (PAU). Using a cross-sectional dataset (N = 767), I conducted a mediation analysis which confirmed that PSU significantly mediates the relationship between ADHD symptoms and PAU. Individuals with higher ADHD symptomatology are more likely to engage in problematic smartphone use, which in turn increases the risk for problematic alcohol consumption. While I hypothesized that earlier age of smartphone use onset would strengthen this mediation effect, the moderated mediation analysis did not yield significant results. The findings underscore the importance of considering behavioral addictions—especially PSU—as potential precursors to substance use problems in ADHD populations. This offers implications for early prevention strategies that target digital media habits as a modifiable risk factor.