as various stages of the smoking trajectory (Audrain-McGovern et al., 2011; Dierker and Donny, 2008; McKenzie et al., 2010; Leventhal et al., 2012). Smokers experience more depressive symptoms, a higher prevalence of lifetime MDD, and more depressive episodes than non-smokers (Wiesbeck et al., 2008; Wilhelm et al. 2006; Ziedonis et al., 2008). Alcohol use has also been linked to depression. A recent study suggests a dose-response relationship between alcohol disorder severity and depression: incidence of depressive disorders was 4% in individuals who met none of the DSM-5 alcohol use disorder criteria and increased to 45% in individuals who met all ten criteria (Boschloo et al., 2012). Similarly, marijuana use has been shown to co-occur with depression. National epidemiologic data indicate 29% of those with lifetime marijuana abuse and 47% of those with marijuana dependence met lifetime criteria for MDD (Conway, 2006). Additionally, marijuana use, especially heavy use, has been shown to be associated with depression among adolescents in the general population (Fergusson et al., 2002; Patton et al., 2002; Rey et al., 2002).
