This analysis examined the possible synergistic effect of exposure to the National Youth Anti-Drug Media Campaign and a classroom-based drug prevention curriculum among 9th grade students participating in a randomized trial of ALERT Plus. A total of 45 South Dakota high schools and their middle-school feeder(s) were randomly assigned to an ALERT condition (basic prevention curriculum delivered in 7th and 8th grades), an ALERT Plus condition (basic curriculum with booster lessons added for 9th and 10th grades), or a control condition. Marijuana use in the past month was significantly less likely among ALERT Plus students reporting at least weekly exposure to anti-drug media messages. The National Youth Anti-Drug Media Campaign may have led to reductions in marijuana use among youth who simultaneously received school-based drug prevention.