We identified a significant G x I interaction from ages 12–18. Figure 2 illustrates this interaction by showing the simple intervention condition effects for adolescents with the TT genotype versus A allele carriers. The left panel displays the intervention condition effect for adolescents with the TT genotype and shows that random assignment to the intervention condition significantly reduced alcohol misuse for these youth from ages 12.5 to 17, with the intervention effect peaking around age 13.5. The right panel shows the intervention condition effect for adolescents carrying the A allele and reveals that the intervention did not appear to significantly reduce alcohol misuse for these youth at any age. The confidence intervals of intervention effect sizes for TT genotype and A carrier youth did not overlap between the ages of 13–16, suggesting that differences in the intervention effect by GABRA2 genotype were most pronounced during this age period.
