The relationship between social media use and youth mental health has become one of the most urgently debated questions in contemporary public health and psychology. Concerns that have animated academic discourse since early correlational studies linking smartphone use to adolescent depression and anxiety have acquired new political urgency as Australia enacted age-based social media restrictions in 2025, UK parliamentary committees called for similar measures, and India’s National Commission for Protection of Child Rights flagged excessive social media use as a primary risk factor for adolescent mental health deterioration. Yet the pathway from social media exposure to psychological distress is neither simple nor uniform: heavy use does not uniformly produce distress, and the mechanisms through which social media features — algorithmic engagement maximisation, infinite scroll, notification frequency, social comparison affordances — convert use into addictive behaviour that then drives mental health consequences remain incompletely specified in the Indian young adult context.This study examines the antecedent-to-consequence chain through a gender-moderated structural equation model applied to survey data from college students across twelve institutions in Tamil Nadu, Andhra Pradesh, and Maharashtra. The Social Media Addiction Scale – Short Version (SAS-SV) operationalises addictive social media use as the key mediating construct between platform use characteristics (daily screen time, fear of missing out, social comparison orientation, notification frequency) and psychological distress outcomes measured by the Depression Anxiety Stress Scale-21 (DASS-21). This dual-scale combination allows the study to distinguish between volume of use — a morally neutral behavioural indicator — and addictive use characterised by loss of control, preoccupation, and functional impairment, which theory and prior evidence indicate is the proximal driver of mental health harm.The study’s Indian institutional context adds geographic specificity to a literature dominated by Western samples where social media platform distribution, cultural norms around social comparison, and generational expectations of digital connectivity differ substantially from the Tamil Nadu and Andhra Pradesh college environment in which Instagram’s Reels format and WhatsApp group pressure dynamics operate within frameworks of collectivist family obligation and academic achievement anxiety that have no direct analogue in the populations from which most published SAS-SV and DASS-21 validation studies are drawn.