There are three striking distinctions between alcohol and the other two substances with respect to their associations with CSA. First, the decrease with age in CSA-associated risk for use was much more gradual for cigarettes and cannabis. Second, the estimated risk associated with CSA in the youngest age range, after adjusting for familial influences, was more than twice as high for alcohol than for cigarettes or cannabis. Third, there was a significant degree of overlap between the contributions of CSA and familial influences on early use of cigarettes and cannabis, as indicated by the significant decreases in HRs from Model 1 to Model 2 for the youngest age ranges. There was no change in the estimate of CSA-associated risk for very early use of alcohol after controlling for genetic and shared environmental influences, indicating that familial risk factors that co-occur at elevated rates in families affected by CSA did not account for the association. The relative influence of familial risk (represented by co-twin early use in the models) on initiation of use was also notably lower for alcohol compared to cigarettes and cannabis.
