Independent of genetic considerations, environmental factors are thought to contribute to 40-50% of variation in problematic cannabis use (Verweij et al., 2010). Abuse, particularly during childhood, has been reliably associated with substance use problems in both adolescence and adulthood (see Simpson & Miller, 2002, for review). Childhood sexual abuse (CSA), in particular, is associated with increased adolescent and adult substance use and misuse, with one study suggesting a 2-fold increased hazard of cannabis use disorders in individuals exposed to CSA (Duncan et al., 2008). Similarly, a longitudinal study found that, even after controlling for covariates (including socioeconomic status, other childhood adversity, parental separation, and parental history of offending), exposure to CSA was significantly predictive of alcohol and other substance use disorders by age 16 to 18 years (Fergusson, Horwood, & Lynskey, 1996). Furthermore, risk for substance use and disorders is elevated in twins exposed to CSA relative to their genetically related unexposed co-twin, underscoring the importance of environmental experience (Myers & Prescott, 2000; Nelson et al., 2006).
