Substance-Induced Depression and Independent Depression in Proximal Risk for Suicidal Behavior

Objective: Major depressive episodes may be substance induced or occur independent of substance use. Studies of the roles of substance-induced depression (SID) and independent depression (IND) in suicidal behavior are limited to retrospective reports. The purpose of this study was to examine proximal (i.e., acute) risk for suicide attempts associated with SID and IND. Method: Individuals who had attempted suicide (n = 100) and nonsuicidal controls (n = 100) matched for site were recruited from residential substance use treatment programs. Participants were ages 18 and older and screened positive for potential alcohol use disorder. Validated semistructured interviews were used to assess SID, IND, and suicide attempts. Analyses of individual-level risk for attempts were based on multivariate logistic regression that adjusted for risk factors. Population-level attributable risk (PAR) fractions for suicide attempts were also calculated to provide estimates of the percentage of attempts in the study population attributable to SID and IND, respectively. Results: SID was identified in 60% of attempters and 35% of controls and IND in 13% of attempters and 3% of controls. Both variables conferred risk for suicide attempt (SID: odds ratio [OR] = 3.73, 95% CI [1.84, 7.58]; IND: OR = 10.38, 95% CI [2.48, 43.49]. PAR for suicide attempts associated with SID and IND was 0.44 and 0.12, respectively. Conclusions: Both SID and IND confer proximal risk for suicide attempts after adjusting for other risk factors. SID also contributes substantial risk in this population overall. Future research should test the hypothesis that IND confers greater risk than SID at the individual level.