In addition to genetic risk, affiliations with cannabis-using peers are believed to be amongst the leading contributors to persistent cannabis use8,11,24,25. However, results from longitudinal samples remain mixed (e.g.,7). While peer use is readily viewed as an “environmental” agent of risk, it can also represent heritable aspects of underlying behavior, with at least one study suggesting a heritability of 25–28% for general peer group deviance, a broad measure including peer marijuana use26. That study also found that about 50–78% of the genetic variance in peer group deviance was attributable to genetic factors related to cannabis use27–29. Another study30 reported that the heritability of perceived peer alcohol use ranged from 7% at age 12–14 up to 38% by age 18, and that the relationship between peer alcohol use and one’s own alcohol use was attributable to genetic factors with a correlation of 0.83. Taken together, these observations raise the possibility that polygenic risk for cannabis use may interface with peer cannabis use in several possible ways, ranging from a main effect to a potential interactive effect. To our knowledge, these hypotheses remain untested.
