Purpose <p>The transition from common initial substances (IS: alcohol, nicotine, cannabis) to more dangerous drugs (MDD) is a critical public health issue in adolescence. This study investigates the distinct roles of social exposure and affective proximity to individuals with substance use disorders (SUD) in relation to this pattern.</p> Methods <p>Data were collected from 822 Italian high school students via an anonymous self-report questionnaire. This cross-sectional study captured retrospective information on the age of substance use initiation alongside data on current use levels. Using structural equation modeling (SEM), we tested a theoretical model assessing the associations between perceived substance use, affective proximity to SUD, and MDD use, with early and current use of IS as mediating variables.</p> Results <p>The model revealed significant and distinct associations. Perceived marijuana use was strongly associated with affective proximity to individuals with SUD. Early IS initiation was significantly associated with perceived marijuana use, affective proximity to SUD, school grade, and sex. Current IS use was significantly associated with early IS initiation and perceived marijuana use. MDD use was most strongly associated with perceived MDD use, followed by early IS initiation, current IS use, and, negatively, by perceived marijuana use and affective proximity to SUD.</p> Conclusion <p>Adolescent MDD use appears to be associated with a dual social mechanism: general normalization of substance use behaviors, and exposure to substance-specific social networks. Prevention strategies should therefore address both broad social normalization processes and the specific risks associated with exposure to networks where severe substance use patterns are prevalent.</p>