PTSD and substance use problems, such as alcohol and cocaine dependence, are complex disorders that commonly co-occur [5, 55]. However, gaps in knowledge exist regarding the reasons for this link between PTSD and substance use disorders. One theory, the shared-liability model, suggests that individuals with co-occurring PTSD and substance use problems have shared risk factors, such as genetic risk [6, 8]. While studies have shown significant genetic overlap (rG = 0.35) between PTSD and alcohol dependence [8], it is important to determine potential shared risk factors that may further link these two disorders. Few studies have investigated associations between PTSD-PRS and other commonly co-occurring disorders [56]. This is the first study to our knowledge that has shown associations between polygenic risk of PTSD and alcohol and cocaine dependence in a sample densely affected with alcohol use disorders. The PGC-PTSD PRS accounted for 1.3%, 1.1%, and 0.6% of the variability in PTSD, alcohol dependence and cocaine dependence, respectively. While effect sizes are quite modest, these results extend previous research that have shown significant genetic correlations between PTSD and alcohol dependence [6,
