Suicide mortality in the United States exhibits substantial geographical and so-ciodemographic heterogeneity. Yet the role of large-scale social networks in shaping this variation remains underexplored. We integrate data on county-level suicide mortality (2010–2022) and Facebook’s Social Connectedness Index (SCI) to assess how both the risk of suicide mortality and the effect of firearm restriction policies propagate through inter-county social ties. First, using two-way fixed effects regression models with sociodemographic, economic, and spatial controls, we find that a one-standard-deviation increase in (SCI-weighted) suicide mortality in socially connected counties is associated with an increase of 2.78 suicide deaths per 100,000 people in the focal county (95% CI: 1.06-4.50). Second, we examine Extreme Risk Protection Orders (ERPOs) — state-level firearm policies that allow temporary restriction of firearm access for individuals at risk of self-harm — and show that counties with stronger (Facebook) social ties to ERPO-adopting states experience reductions in suicide mortality, even without local policy implementation. Our findings suggest that a one-standard-deviation increase in ERPO social exposure is associated with a decrease of 0.301 suicide deaths per 100,000 people in the focal county (95% CI: 0.480-0.121). This protective association persists after adjusting for geographical proximity and including state-by-year fixed effects that capture time-varying state-level factors. In sum, our findings suggest that social networks can facilitate the diffusion of both harmful exposures and protective interventions. This socio-spatial structuring of suicide mortality underscores the need for network-driven prevention strategies that incorporate social network topology (e.g., SCI-derived influence metrics), alongside more traditional approaches based on geographical targeting.

K.T. has been an associate specialist at Merck Sharp & Dohme LLC from May to August 2023. M.A.R. has served on the advisory committee of a vaccine confidence fund created by Meta and Merck; some of his research has also been funded by Meta. The other authors declare no competing interests.

This study did not receive any funding.

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Institutional Review Board of the University of Pittsburgh waived ethical approval for this work, determining that it does not involve human subjects as defined by DHHS and FDA regulations (Not Human Subjects Research). Informed consent was not required because only de-identified, aggregate data were analyzed and no interaction with individuals occurred.

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