Unveiling the Complexity of Substance Use Disorder: Insights from a Multimethod Investigation

Substance use disorder (SUD) is one of the most challenging psychiatric conditions worldwide. Despite decades of research, its complex nature makes it difficult to fully understand and effectively address. Initially characterized as a moral failing, SUD has revealed itself in recent decades as a multifaceted condition encompassing neurobiological vulnerabilities, psychological processes, social and environmental contexts, and developmental trajectories. It manifests through a variety of cognitive, behavioral, and physiological symptoms that can severely compromise individual functioning and lead to a plethora of negative outcomes. Adding to this complexity, the very definition and diagnostic criteria for SUD have undergone multiple revisions over the past decades. It is highly heterogeneous, with a multifactorial etiology, and pathways and outcomes vary greatly across individuals (APA, 2013). While fascinating, this complexity has profound implications for how addiction is identified, prevented, and treated, and ultimately for how individuals struggling with SUD are supported. The core aim of the present research project is to embrace – rather than reduce – this complexity. To achieve this, the thesis explores SUD from three complementary perspectives: as a risk factor for negative outcomes, as a phenomenon embedded within a broader psychosocial network, and as a negative outcome. By examining these multiple facets, this work seeks to advance a more comprehensive understanding of the disorder and to inform practical prevention and intervention strategies. The thesis is organized into five chapters. Chapter 1 provides a general introduction on the topic, presenting the historical and diagnostic evolution of SUD, reviewing its epidemiology, and presenting the integrative model that frames this research. Chapter 2 reports the first empirical study, which examined substance addiction as a vulnerability factor for suicidal thoughts and behaviors. Chapter 3 presents the second study, which situates alcohol and cannabis use disorders within a psychosocial network that includes psychological distress, suicidal ideation, sociodemographic factors, and social determinants of mental health. Chapter 4 reports the third study, which investigated the role of the big 5 personality traits as necessary conditions for problematic alcohol use across developmental stages. Finally, Chapter 5 synthesizes the findings from all three studies within the integrative framework, interpreting divergent results, and highlighting implications for clinical practice, prevention strategies, and future research.