Some studies have found that the significant associations observed between smoking and suicide persist after controlling for confounders such as psychiatric disorders (e.g. depression, anxiety), (Tanskanen et al. 2000; Breslau et al. 2005; Yaworski et al. 2011) but other have not (Hemmingsson and Kriebel 2003; Kessler et al. 2007; Boden et al. 2008). However, two of these studies were cross-sectional (Kessler et al. 2007; Yaworski et al. 2011) and most of the prospective cohorts did not adjust for psychiatric disorders (Hemenway et al. 1993; Tverdal et al. 1993; Doll et al. 1994; Leistikow et al. 2000; Miller et al. 2000a; Miller et al. 2000b; Iwasaki et al. 2005). Even if several cohort studies have found a positive monotonic association between cigarette smoking and suicide or suicidal behavior, smoking was assessed only at the cohort inception and not updated during the follow-up. The relationship between smoking and depression has been extensively studied, but still remains equivocal (Glassman 1993; Covey et al. 1998). According to a twin study, the association between smoking and depression is not causal but arises largely from other
