Extreme risk protection order policies and homicide risk among cohabitants of handgun owners.

Extreme Risk Protection Orders (ERPO), known as Gun Violence Restraining Orders in California, are designed to reduce gun violence by allowing courts to temporarily remove firearms from individuals who pose a risk to themselves or others. Population-level evidence on their impacts remains limited. We used the Longitudinal Study of Handgun Ownership and Transfer, which links California voter, mortality, and firearm transaction records, to evaluate the impact of California's ERPO law on homicide risk among cohabitants of handgun owners who are not themselves handgun owners. Using a difference-in-differences design, we compared changes in 1-year homicide risks before (2012-2015) and after (2016-2021) policy implementation among adults living with handgun owners vs those in households without known handgun owners. We estimated a 1-year difference of -0.42 (95% CI, -1.86 to 1.02) homicide deaths per 100 000 persons among cohabitants of handgun owners who are not themselves handgun owners, with null findings robust across sensitivity analyses. Though our findings did not suggest substantial population-level protective effects, ERPOs may still reduce risk of homicide among cohabitants of ERPO respondents in ways not detectable at the population level. At the population level, their effectiveness may depend on more frequent or better-targeted use.