Our finding that SA is associated with onset of alcohol, nicotine and cannabis dependence might be interpreted in several ways. First, increased likelihood of substance use disorders, particularly in those with SA, might reflect escalations in substance use for negative affect regulation (i.e. self-medication: Khantzian, 1997; or coping: Esposito-Smythers et al., 2004), as has been noted for mood and anxiety disorders (e.g. Bolton et al., 2009;Crum et al., 2013;Dawes et al., 2008;Robinson et al., 2011). Psychiatric disorders such as MDD, especially in their active form (Breslau et al., 2004), predict nicotine dependence (e.g. (Breslau et al., 1993). Alternatively, this association may reflect a shared liability to behaviors that include negative affect as a component. Negative affect, including depressed mood (e.g. withdrawal) are hallmark features of substance use disorders (Brady et al., 2005) as well as SI and SA. Studies have also suggested that shared genetic influences may be responsible for the comorbidity across MDD and alcohol (Kendler et al., 1993) and nicotine dependence (Edwards et al., 2011;Thornton et al., 2016). However, adjustment for MDD did not abolish our association suggesting
