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

On an average day in 2010, the last year for which national data are available, more than 100 Americans died by suicide; half used firearms (Centers for Disease Control and Prevention (CDC)). Suicide, the tenth leading cause of death among Americans in 2010 (Centers for Disease Control and Prevention (CDC)), occurs at substantially higher rates in rural compared with urban areas, largely due to higher rates of firearm suicide in rural areas (Singh and Siahpush 2002). Prior research using mortality and prescription data from the 1990s explains the rural-urban suicide gradient as largely due to the fact that (in the 1990s) newer antidepressants (largely SSRIs) were less likely to be prescribed in rural than in urban areas (Gibbons et al. 2005). Injury researchers, by contrast, have long observed that the rural-urban gradient in US suicide rates, both during the 1990s and presently, is largely explained by a pronounced gradient in firearm (but not non-firearm) suicide rates and, furthermore, that the firearm-suicide gradient is highly correlated with rates of household firearm ownership (Branas et al. 2004; Miller and Hemenway 1999).

These two key exposures – i.e., firearm ownership and antidepressant prescribing – have been adduced to explain geographic patterns of US suicide mortality more broadly as well. For example, as reviewed previously (Miller and Hemenway 1999;2012; Brent 2001) ecologic studies in the U.S. have linked variation in suicide rates with the distribution of household firearm ownership. These studies have evaluated variation across states, census divisions, and cities, as well as over time, and have found overall suicide rates and firearm suicide rates are positively associated with firearm ownership prevalence. Consistent with these ecologic observations, case-control studies have also linked exposure to firearms in the home with increased risk of suicide overall due to an increased risk of suicide by firearm (Brent 2001; Kellermann et al. 1992; Conwell et al. 2002; Cummings et al. 1997; Wiebe 2003; Shah et al. 2000; Dahlberg et al. 2004; Bailey et al. 1997; Grassel et al. 2003; Kung et al. 2003). Geographic (Gibbons et al. 2005; Grunebaum et al. 2004) and temporal (Olfson et al. 2003) variation in suicide rates has also been linked to variation in antidepressant prescription patterns. While some early studies reported an inverse association between antidepressant prescription rates and overall suicide rates (Grunebaum et al. 2004; Olfson et al. 2003), a later review of nineteen ecological studies from around the world found that less than half observed such an association (Baldessarini et al. 2007). At least one early US study that found an inverse association between antidepressant prescription rates and overall suicide (Olfson et al. 2003) noted that future studies should account for gun ownership if and when such measures became available.

The current study is, to our knowledge, the first to consider the joint contribution of rates of antidepressant prescribing and household gun ownership on suicide mortality in the United States.

We assembled an extensive panel data set from the United States including rates of suicide, antidepressant prescriptions, firearm ownership, and other covariates of interest.

Over the study period, 2001-2004, there were 126,200 suicides in the US of which 67,634 involved firearms (53%). Firearm suicide rates varied 8.4 fold across the 50 states, whereas non-firearm suicide rates varied 2.7 fold (Table 1). The percent of people living in homes with firearms ranged widely, from 8% to 63%. Annual antidepressant prescription rates varied from 20,444 prescriptions per 100,000 people to 68,676 per 100,000 people.

Our study is the first to simultaneously evaluate the effects of firearm ownership and antidepressant prescription rates on the distribution of suicide rates across the United States. Consistent with prior ecologic and individual level studies from the United States (Miller and Hemenway 1999; Miller et al. 2012; Brent 2001; Kellermann et al. 1992; Conwell et al. 2002; Cummings et al. 1997; Wiebe 2003; Shah et al. 2000; Dahlberg et al. 2004; Bailey et al. 1997; Grassel et al. 2003; Kung et al. 2003), we find a robust association between firearm ownership and suicide. Moreover, this association remains significant and undiminished in magnitude after adjusting for antidepressant prescription rates, median income, unemployment rates, and urbanization. This covariation with overall suicides appears to be driven by covariation with firearm suicides.

By contrast, we do not observe a significant relationship between antidepressant prescription rates and completed suicide. Our study finds that where more antidepressants are prescribed per capita, suicide rates are neither higher nor lower than in states with lower prescribing rates, consistent with Gunebaum et al’s (2004) adjusted analyses, but contrary to some findings from Olfson et al. (2003) Olfson et al. observed that regions with average higher adolescent use of antidepressants in 2000, compared with use in 1990, had lower suicide rates in 2000. In their discussion, Olfson et al. noted that because other factors related to suicide risk also changed over the period, studies, such as ours, that examine whether the association between antidepressants and suicide that they report might be confounded by gun prevalence were needed.

Our findings should be considered in light of several possible limitations. First, as an ecological study, our study cannot identify whether the people who completed suicide tended, in fact, to live in homes with guns or to take antidepressant medication. Second, although our state and county-level analyses produce congruent results, our county-level findings could be influenced by county selection. The counties in our study were selected for a single reason: firearm estimates were available in the BRFSS. There is no a priori reason, however, to think this would introduce bias. Indeed, our counties, which tended to be more urban and to have lower household ownership rates than the US as a whole, also had slightly lower suicide rates, driven by fewer firearm suicides per capita (a pattern consistent with our general finding that where there are more guns there are more suicides).

The current study does not, it should be underscored, rule out the possibility that antidepressants may have a beneficial (or a harmful) effect on suicide rates, but rather indicates that prior ecological evidence of the effectiveness of antidepressants in reducing US suicide rates were confounded by a failure to adjust for firearm ownership rates. The current paper also demonstrates the robust relationship between firearms and suicide, adds to the growing literature connecting access to firearms in the home with completed suicides, and lends further support to the importance of integrating means restriction approaches into US suicide prevention policy.