Adolescents' use of alcohol, tobacco, and marijuana poses a significant public health challenge, particularly in Chile, where early onset and peer influence are major factors. This study leverages longitudinal social network data from schools in Chile, Colombia, Italy, and the Netherlands to examine the reciprocal effects of peer relationships and substance use. It explores three dimensions: how substance use affects friendship formation, the moderating roles of peer pressure susceptibility and depression, and the dynamics of drinking and smoking networks. By adopting an innovative network analysis approach, this research aims to inform more effective prevention strategies and foster international collaborations, ultimately contributing to better understanding and addressing adolescent substance use across diverse contexts.