Abstract
Substance use disorder (SUD) is a multifaceted crisis shaped by the interaction of biological, psychological, relational, and structural forces across the life course. Despite the proliferation of integrated SUD frameworks, existing models insufficiently address stage-based progression, institutional barriers, socio-structural determinants, and the lived mechanisms connecting vulnerability to initiation, entrenchment, crisis, and recovery. This study addresses these gaps through qualitative content analysis of 991 in-depth interview transcripts drawn from Soft White Underbelly, a publicly accessible YouTube series documenting first-person narratives of individuals experiencing significant social marginalization and long-term substance use. Guided by grounded theory coding procedures and large language model-assisted text processing across approximately 3.9 million words, the analysis produced 100 open codes, 27 axial codes, and 8 selective codes, organized into an eight-stage sequential model of SUD progression spanning Early Developmental Vulnerability, Initiation Pathways, Survival and Street Adaptation, Dependence and Entrenchment, Crisis and Acute Risk, Treatment Exposure and Barriers, Recovery and Reorientation, and Relapse or Stabilization. The model advances existing theory by specifying the connecting mechanisms through which each stage generates conditions for the next. Key findings demonstrate how early adversity produces cascading vulnerability, how cognitive distortions sustain treatment resistance, and how compounding exclusion loops, combining stigmatizing beliefs, structural access barriers, and missing identification documents, systematically remove individuals from care regardless of motivational readiness, making structural reform as essential as motivational intervention. The model provides an empirically grounded, stage-specific framework for designing prevention and intervention strategies aligned with the lived realities of those most severely affected by SUD.