| Sumario: | Objectives. We examined the cognitive and behavioral effects of the National Youth Anti-Drug Media Campaign on youths aged 12.5 to 18 years and report core evaluation results. Methods. From September 1999 to June 2004, 3 nationally representative cohorts of US youths aged 9 to 18 years were surveyed at home 4 times, Sample size ranged from 8117 in the first to 5126 in the fourth round (65% first-round response rate, with 86%-93% of still eligible youths interviewed subsequently). Main outcomes were self-reported lifetime, past-year, and past-30-day marijuana use and related cognitions. Results. Most analyses showed no effects from the campaign. At one round, however, more ad exposure predicted less intention to avoid marijuana use (γ= -0.07; 95% confidence interval [Cl]=-0.13, -0.01) and weaker antidrug social norms (γ=-0.05; 95% Cl=-0.08, -0.02) at the subsequent round. Exposure at round 3 predicted marijuana initiation at round 4 (γ = 0.11; 95% Cl=0.00, 0.22). Conclusions. Through June 2004, the campaign is unlikely to have had favorable effects on youths and may have had delayed unfavorable effects. The evaluation challenges the usefulness of the campaign. (Am J Public Health. 2008;98:2229-2236. doi:10.2105/AJPH.2007.125849)
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