Several outcomes in this meta-analysis demonstrated significant between-study variability in effect sizes and thus complicate inferences. Sensitivity analyses and moderator analyses both identified the study by Wilens et al36 as the source of heterogeneity in effects of stimulant medication and later nonspecific drug abuse or dependence. Unlike the predominantly male samples, this all-female study suggested a potentially protective role of stimulant medication treatment for drug abuse or dependence than did the others. Sex accounted for more than 75% of the variation in effect sizes for this outcome, suggesting that sex differences may be important to consider for stimulant medication and substance use outcomes. Most longitudinal research on ADHD is predominantly male (see the studies by Biederman et al27 and Hinshaw43 for key exceptions), and thus the specific effect of treatment among females with ADHD merits further study.
