Objectives: The study aimed at extending the general finding from prior research, that adolescents' intentions to use and actual use of doping substances are influenced by a set of beliefs concerning doping use, by also evaluating whether these belief systems influence changes in doping use over time. In addition, the present study also examined the novel hypothesis that adolescents' appraisals of interpersonal encounters in which they are solicited to use doping substances would moderate the relations linking beliefs to doping intentions and doping use. Design and Methods: Nearly 900 adolescents (50.6% males, mean age = 15.6) provided longitudinal data on their attitudes, subjective norms, behavioral control, self-regulatory efficacy, moral disengagement, intentions and past substance use. They also rated the intentions of counterparts who hypothetically solicited them to use substances. Results: The multivariate analysis of the relations among the key variables revealed that belief systems influenced adolescents' doping intentions, accounting for nearly 50% of their variance. Furthermore, doping intentions, in turn, longitudinally influenced and accounted for nearly 75% of the variation in adolescents' doping use. Finally, additional multi-group analyses revealed that the overall effects on adolescents' doping intentions were particularly strong (R(2) = 52) among those who made risky situational appraisals, as compared to those who showed no-risk appraisals (R(2)=.13). Conclusions: The findings of the study were consistent with the hypothesis that adolescents' doping use is regulated by doping-specific belief systems. They also suggest that the relations linking doping-specific beliefs and intentions are enhanced among adolescents who preemptively tend to assign a positive meaning to interpersonal exchanges in which others solicit doping use. Implications for prevention interventions focusing on the processes of social influences are discussed. (C) 2010 Elsevier Ltd. All rights reserved.