Experiencing violence and other predictors of within-person same-day use of multiple substances in youth: a longitudinal study in emergency settings.

Although experiencing violence is a risk factor for substance use among youth, its association with same-day use of multiple substances (a form of polysubstance use) and mitigating factors is less well understood. To identify whether prosocial factors modified the effect of experiencing violence on the frequency of same-day use, and examine gender-specific risk/protective factors for same-day use. We analyzed longitudinal data from a cohort of youth who use drugs aged 14-24 ( = 599; 58% male) presenting to an urban emergency department between 2009-2011 and assessed biannually for two years. Using Poisson-generalized linear models with person-level fixed effects, we estimated within-person associations between self-reported experiencing violence and same-day use and analyzed gender and peer/parent support as effect modifiers. We adjusted for negative peer influence, parental drug and alcohol use, family conflict, anxiety and depression, and age. Overall, positive parental support corresponded to lower rates of same-day use (rate ratio [RR]:0.93, 95% CI:0.87-0.99) and experiencing violence was associated with higher rates of same-day use (RR:1.25, 95% CI:1.10-1.41). Violence exposure was a risk factor among males (RR:1.42, 95% CI:1.21-1.66), while negative peer influences and parental substance use were risk factors among females (RR:1.63, 95% CI:1.36-1.97 and RR:1.58, 95% CI:1.35-1.83, respectively). Positive peer support reduced the association between violence exposure and same-day use among males (RR:0.69, 95% CI:0.57-0.84,  < .05). Tailored interventions may address gender differences in coping with experiencing violence - including interventions that promote parental support among males and reduce influence from parental substance use among females.