BACKGROUND: Substance use disorders are a major risk factor for suicide. However, less is known about specific risk factors for suicide in people with substance use disorders.

METHODS: This population cohort study assessed suicide among people treated for drug use disorders in Denmark 2000-2010, and described risk factors for completed suicide. Data from 27,942 individuals enrolled in treatment were linked to national registers and matched with controls without drug use disorder and with (n = 138,136) or without psychiatric history (n = 1574). Competing risk regression was used to identify risk factors of completed suicide.

RESULTS: There were 163 suicides among patients with a history of drug treatment (0.6% of patients). Increased risk was associated with younger age at enrolment (hazard ratio [HR] = 0.97, 95% confidence interval (CI): 0.95, 0.98), history of psychiatric care (HR = 1.96, CI 95%: 1.39, 2.77), opioid use (HR = 1.81, 95% CI: 1.23, 2.68), and alcohol use (HR = 1.56, 95% CI: 1.09, 2.23). Lower risk was associated with cannabis use (HR = 0.69, 95% CI: 0.50, 0.96). Compared with age- and gender-matched controls without a history of treatment for substance use disorders or recent psychiatric care, the standardized mortality ratio due to suicide was 7.13 for people with drug use disorder without a history of psychiatric care (95% CI: 5.81, 8.44), 13.48 for people with drug use disorder and psychiatric history (95% CI: 9.75, 17.22), and 13.61 for people with psychiatric history only (95% CI: 6.72, 20.50).

CONCLUSIONS: Risk of suicide is increased among people with drug use disorders. Access to treatment for co-morbid mental health problems for people with drug use disorders could potentially reduce risk of suicide.