This dissertation represents the first effort to examine the relevance and effects of ambivalence in the contexts of adolescent marijuana use and anti-drug communication targeting adolescents. Jointly motivated by the bivariate model of attitude (Cacioppo et al., 1997) and the attitude strength perspective in previous ambivalence research (Krosnick & Petty, 1995), this dissertation investigated the effects of ambivalence on both adolescents' marijuana use behavior and their processing of anti-drug messages. In the behavioral domain, this dissertation tested the hypothesis that ambivalence could weaken the relationships between adolescents' attitudes toward marijuana use and their intentions to use and actual use behavior. In the information processing domain, this dissertation tested two related hypotheses: First, initial ambivalence about marijuana use would motivate adolescents to engage in systematic processing of anti-drug messages. Second, initial ambivalence about marijuana use would make adolescents susceptible to the influence of anti-drug messages. Analyses of data from a large-scale national survey (National Survey of Parents and Youth, NSPY; Round 1 N = 5,100; Round 2 N = 5,101; Round 3 N = 5,325) and an independent smaller-scale survey (N = 322) produced relatively strong evidence that ambivalence plays an important moderating role in the relationship between adolescents' marijuana attitudes and their intentions to use marijuana. For high risk adolescents, ambivalence shows itself to be an anti-drug factor eventually leading to lower intention (and possibly decreased behavior), whereas for low risk adolescents, ambivalence shows itself to be a pro-drug factor eventually resulting in stronger intention (and very likely increased behavior). An experiment was conducted to test the information processing hypotheses. In this experiment (N = 382), adolescents were exposed to either a strong or a weak anti-drug brochure. After exposure, they completed measures assessing amount and valence of processing and marijuana-related cognitions. Results from the experiment showed relatively consistent support for the general vulnerability hypothesis - high ambivalence participants reported greater agreement with the anti-drug messages and more anti-drug positions on intention, attitude, and authority approval. The systematic processing hypothesis, on the other hand, received no clear support. Findings of this dissertation have important implications for anti-drug communication campaigns. First, evaluation of future anti-drug communication campaigns should consider including ambivalence as an additional outcome variable to enable more accurate assessment of campaign effect. Second, future anti-drug communication interventions may consider purposely targeting ambivalence in their messages so as to exploit not only the moderating effect of ambivalence but also ambivalent attitudes' general pliability to persuasion.
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