risky behaviors, including sexual behavior as suggested by prior work in adolescent males in Thailand (Ruangkanchanasetr et al., 2005, Liu et al., 2006, Assanangkornchai et al., 2007), the effect of law enforcement focusing on males which could recruit male MA-users into the treatment program earlier than females, and the societal difference in the response to substance use among males compared to females in terms of attitude toward males as having more severe and problematic substance use and negative consequence than females. It is worth noting, however, that despite an earlier age of MA use onset in males, females more commonly met criteria for MA dependence. The dissociation is remarkable, insofar as early age of onset has often been suggested to associate with increased chances of dependence. We speculate that differences between males and females in our treatment cohort may account for our finding. For example, females in our cohort were older at the time of recruitment, which might associate with later MA onset compared to males. In addition, we speculate that age of onset and sex difference might contribute to severity of MA dependence independently. Nevertheless, earlier age of onset is still associated with the occurrence of MA dependence in
