Darvishi et al [9] conducted a meta-analysis in 2015 to estimate the alcohol-related risk of suicide. They assessed 31 epidemiological studies and reported that alcohol use dependence increases the risk of suicidal ideation 1.86 fold (95% CI: 1.38, 2.35), the risk of suicide attempt 3.13 fold (95% CI: 2.45, 3.81); and the risk of suicide death 2.59 fold (95% CI: 1.95, 3.23). Another meta-analysis was conducted by Poorolajal et al [11] in 2016 to address the association between substance use disorder and suicidal behaviors. They assessed 43 epidemiological studies and concluded that the substance use disorder was significantly associated with an increased risk of suicidal ideation (OR 2.04; 95% CI: 1.59, 2.50); suicide attempt (OR 2.49; 95% CI: 2.00, 2.98) and suicide death (OR 1.49; 95% CI: 0.97, 2.00). It is likely that part of the association between smoking and suicide reported in this meta-analysis may be explained by the confounding effects of these well-known risk factors. However, another part of the association may be the result of the effect of smoking itself that may increase the risk of suicide
