A prospective study of the paradoxical relationship between impulsivity and lethality of suicide attempts

Background: Biological studies suggest that lower serotonergic activity is associated with both greater suicide lethality and impulsive personality traits. These results may lead to the conclusion that impulsivity in the attempt should be associated with greater lethality. However, Klerman's review of epidemiologic suicide studies suggests an inverse relationship between impulsivity and lethality. This seemingly paradoxical relationship between impulsivity and lethality has not been explored in large representative clinical samples of suicide attempts. Method: During 1996 to 1998, 478 individuals who attempted suicide were studied in a general hospital in Madrid, Spain. Impulsivity was measured as described in the literature by combining 2 items of Beck's Suicidal Intent Scale (active preparation for attempt and degree of premeditation). Lethality of the attempt was assigned 1 of 4 levels according to the need for medical and/or psychiatric treatment. Results: More than half of the attempts were impulsive (55%; 95% confidence interval [CI], 51% to 59%), approximately one fourth of the attempts had an intermediate level of impulsivity (28%; 95% CI, 24% to 32%), and approximately one sixth of the attempts were not impulsive (17%, 95% CI, 13% to 21%). There was an inverse association between the impulsivity and lethality of the suicide attempt (χ² = 62.639, df = 6, p < .0001). The most impulsive attempts tended to result in less morbidity, while the less impulsive attempts tended to be more lethal. Conclusion: If the inverse relationship between impulsivity and lethality is replicated in other large and representative samples, new studies will be needed to clarify the complex interactions between the clinical dimensions (lethality, impulsivity as a state, and impulsivity as a personality trait) and the biological correlates (particularly serotonergic function) of suicidal behavior.