In this study, the authors were interested in clarifying the interrelationship of parents’ and friends’ drug use as an influencing factor on adolescent substance use risk. Previous research has documented that teens’ risk of substance use is high if both their friends and their parents use drugs. However, how the two variables of parent drug use and friend drug use interact is not understood. As such, the authors first explored whether the use of a specific drug by both the parents and the friends was related to adolescent use of a specific substance. Second, they tested interactions between parents’ and friends’ drug use as influencing factors on adolescent drug use. Finally, the authors tested friends’ influence on adolescent drug use with two groups of adolescents: adolescents whose parents used drugs and adolescents whose parents did not use drugs. Results of logistic regression and multiple group structural equation modeling supported previous research that showed a parental and peer group influence on the substance use risk of adolescents. This study further demonstrated that parents served as a buffer to friends’ influence over adolescent substance use. Those adolescents whose parents did not use drugs were more likely not to use drugs even when their friends’ did use substances. This research indicates that parents should be an integral part of adolescent substance use prevention programs. Tables, figures, references