Cigarette Smoking, Suicidal Behavior, and Serotonin Function in Major Psychiatric Disorders

OBJECTIVE: Cigarette smoking is associated with a higher risk for suicide and attempted suicide, but psychopathological or biological explanations for this association have not been explored. Lower serotonin function and impulsive/aggressive traits are associated with suicidal acts, including completed suicide. The authors hypothesized that the relationship that may exist between cigarette smoking and suicidal behavior may be associated with lower serotonin function and the presence of impulsive/aggressive traits. METHOD: Study subjects were 347 patients with a psychiatric disorder (175 with depression, 127 with schizophrenia, and 45 with other disorders). Fifty-three percent of the subjects (N=184) had a lifetime history of suicide attempt, and 47% (N=163) had never attempted suicide. Smoking behavior, lifetime suicidal behavior, and psychopathology were assessed. Serotonin function was assessed in a subgroup of patients with depression (N=162) by using a fenfluramine challenge test and/or measurement of CSF levels of 5-hydroxyindoleacetic acid. RESULTS: Among all patients, smokers were more likely to have made a suicide attempt (adjusted odds ratio=2.60, 95% confidence interval=1.60–4.23) and had higher suicidal ideation and lifetime aggression scores, compared with nonsmokers. An inverse relationship was observed between amount of cigarette smoking and both indices of serotonin function. CONCLUSIONS: The association between cigarette smoking and the presence and severity of suicidal behavior across major psychiatric disorders may be related to lower brain serotonin function in smokers with depression. Further investigation is required to replicate these findings, to measure serotonin function in patients with disorders other than depression, and to test potential therapeutic effects of serotonin-enhancing treatments on both smoking behavior and suicide risk.