Effects of anti-tobacco and anti-marijuana TV advertisements on explicit (i.e., semantic differential ratings) and implicit (i.e. Implicit Association Test, IAT) attitudes toward tobacco and marijuana were compared. Two hundred twenty nine, 18- to 19-year-old U.S. college students were randomly assigned to anti-tobacco or anti-marijuana PSA viewing conditions. Participants completed a short survey on attitudes to tobacco and marijuana. Afterwards they watched 15 PSAs embedded in a 15-min science program. At the end, all participants completed IAT for marijuana, IAT for tobacco and the assessment of explicit attitudes. Results of ANCOVA revealed a significant interaction between type of TV PSAs watched and implicit attitudes, F(1,223)=7.12, p<0.01 when controlling for preexisting attitudes to both substances; the implicit attitudes were more negative toward the substance that corresponded to the content of advertisements watched (i.e., anti-tobacco or anti-marijuana). However, analogical analysis on explicit measures showed that attitudes to marijuana became less negative among students that watched anti-marijuana ads than the group with anti-tobacco ads, F(1,222)=5.79, p<0.02. The discussion focused on the practical and theoretical implications of the observed dissociation between implicit and explicit attitudes to marijuana after the exposure to anti-marijuana PSAs.