Prior research on delinquent peer association and adolescent drug use predominantly examines the direct link between the two factors from the differential association/social learning perspective. The current study, based on survey data among 8,027 secondary school students sampled from three major cities in the Greater China Region, aims to elucidate this relationship further by identifying key mediators derived from several major criminological theories and perspectives, including social learning theory, lifestyle/routine activity theory, general strain theory, and the opportunity perspective. This study finds that significant mediators include pro-drug use attitudes, crime victimization, and drug availability, with pro-drug use attitudes exerting the most substantial influence on adolescent drug use. These results underscore the complexity of the relationship between delinquent peer association and adolescent drug use, advocating for a multifaceted theoretical approach for comprehensive understanding.