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Drug prevention campaigns commonly seek to change outcome expectancies associated with substance use, but the effects of violating such expectancies are rarely considered. This study details an application of the expectancy violation framework in a real world context by investigating whether changes in marijuana expectations are associated with subsequent future marijuana intentions. A cohort of adolescents (N = 1,344; age range = 12-18 years) from the National Survey of Parents and Youth was analyzed via secondary analysis. Nonusers at baseline were assessed 1 year later. Changes in expectancies were significantly associated with changes in intentions (p < .001). Moreover, in most cases, changes in expectancies and intentions had the strongest relationship among those who became users. The final model accounted for 31% of the variance (p < .001). Consistent with laboratory studies, changes in marijuana expectancies were predictive of changes in marijuana intentions. These results counsel caution when describing negative outcomes of marijuana initiation. If adolescents conclude that the harms of marijuana use are not as grave as they had been led to expect, intentions to use might intensify.