We also examined whether a history of SI or SA was associated with onset of substance use and dependence. Here, an interesting divergence between SI and SA was noted. Unlike the cross-sectional findings, a prior history of SI was associated with a reduced likelihood of the onset of alcohol, nicotine and cannabis use (OR=0.71 – 0.77). This was not the case for SA. Because onset of SI and substance use tend to cluster around similar ages (Supplemental Figures S1A, S1B, S1C, S2A and S2B), we presume that these “protective” effects might reflect a trajectory indicative of escalating problems with internalizing behaviors (e.g. MDD) that are independent of experimentation or self-medication with substances. Early SI might represent significant depressed mood which may also reduce the chance that individuals will interface with delinquent peer groups (potentially, due to peer rejection) who might have otherwise promoted substance use (Hussong et al., 2011). In fact, a prior study of these data show similar protective effects of a score assessing difficulties with family and peers on age of onset of alcohol use (Kuperman et al.,
