Background: Although an association between smoking and suicide has repeatedly been shown, information about a modifying influence of smoking on other risk factors for suicide is lacking.
Methods: Axis I and Axis II disorders, sociodemographic factors, and tobacco use were assessed by a semi-structured interview including the Structured Clinical Interview for DSM-IV Axis I (SCID-I) and Personality Disorders (SCID-II) in 163 suicides (mean age 49.6+/-19.3 years; 64.4% men;) by psychological autopsy method and by personal interview in 396 living population-based control persons (mean age 51.6+/-17.0 years; 55.8% men).
Results: Smoking status (current smokers, lifetime non-smokers, and former smokers) differently modifies the effects of psychiatric disorders and sociodemographic variables on suicide risk. Former and current smoking modified suicide risk associated with affective disorders, but only current smoking increased suicide risk for substance use disorders. Ex-smokers with affective disorders, particularly with major depression, had less increased suicide risk than current smokers and non-smokers with affective disorders. Estimated suicide risks for personality disorders and 'no professional training' were strongly increased by smoking.
Limitations: Due to the small size of some of the subgroups, confidence intervals are wide. Therefore, precise risk estimation is not possible.
Conclusions: Clinicians should interpret smoking as an indicator of increased risk of suicide for individuals with substance use disorders, personality disorders, and adverse social factors. Further studies are needed to investigate the effects of smoking cessation on suicide risk of patients with psychiatric disorders such as major depression and substance use disorders.