Second, the “environmental” risk factor in our study, perceived peer cannabis use explained up to 11.3% of the variance in trajectory membership. This suggests that, although genetics certainly plays a role in the progression of cannabis use, established environmental influences such as peer use are better predictors of cannabis use than PRS at the moment, and this is likely to be true for other complex behavioral traits as well. Uniquely, genetic propensity to cannabis use was also associated with greater perceived peer engagement in cannabis use. Consistent with prior heritability studies, this finding of genetic contributions to perceived peer use might reflect gene-environment correlation48,49 or causal processes, such as Mendelian randomization50. However, both PRS and peer use remained significantly associated with class membership when simultaneously modeled suggesting some independent effects.
