The results support Belsky and colleagues’ (2007) differential susceptibility hypothesis in which variants of specific genes, including DRD4, are proposed to render individuals more susceptible to the surrounding environment whether it is characterized by high positivity or high risk. The finding that, after exposure to the protective processes that SAAF–T offered, carriers of at least one l allele as well as adolescents carrying two nonsusceptibility s alleles of DRD4 evinced less substance use over time than did similar youths in the control condition supports differential susceptibility predictions. If supported on a broader basis, these results imply that general estimates of intervention effects on health-relevant outcomes both under- and overestimate efficacy. The estimates underestimate efficacy for genetically susceptible individuals and overestimate it for those without genetic susceptibilities. Clearly, more genetically informed prevention/intervention research is required to confirm this conclusion.
