Explaining geographic patterns of suicide in the US: the role of firearms and antidepressants

BACKGROUND Suicide rates vary more than 3-fold across the fifty states. Previous ecological studies have pointed, separately, to covariation of suicide mortality with rates of a) household firearm ownership, and b) antidepressant prescriptions. METHODS An ecologic study using panel data from 2001-2005 was used to evaluate the joint and separate association of household firearm ownership and antidepressant prescription rates with the distribution of suicide rates across the United States. Key exposures were household firearm ownership prevalence (using data from the 2004 Behavioral Risk Factor Surveillance System) and antidepressant prescription rates (using data supplied by IMS health). Negative binomial mixed-effect models were used to estimate the association between household firearm ownership prevalence and antidepressant prescriptions rates and state level suicide rates (using data from the National Vital Statistics System), overall and by method of suicide (firearm vs. non-firearm). Sensitivity analyses examined analogous county-level data for those counties for which firearm ownership measures were available. All analyses were adjusted for median income, unemployment rate, and percent of population in urban areas. RESULTS In adjusted analyses, household firearm prevalence is significantly associated with overall suicide rates (adjusted incidence rate ratio (IRRa) = 1.28, 95% confidence interval (CI): 1.18, 1.38) and firearm suicides rates (IRRa = 1.61, CI: 1.45, 1.80), but not with non-firearm suicide rates (IRRa = 1.05, 95% CI: 0.95, 1.16). By contrast, adjusted analyses find no relationship between suicide rates and antidepressant prescription rates. Findings from county-level analyses were consistent with state-level results. CONCLUSION The prevalence of household firearm ownership is strongly and significantly associated with overall suicide rates, due to its association with firearm suicide rates. This association is robust to consideration of the role of antidepressant prescription rates. A relationship between antidepressant prescription rates and suicide rates was not observed before or after adjusting for firearm ownership.