Aside from buybacks and laws that directly reduce gun ownership, firearm laws can only have an effect on the suicide rate of populations not previously exposed to firearms.
Most firearm laws are not passed with reducing suicides as their primary intent, thereby attenuating any relationship between said laws and suicide reduction.
Laws passed in Israel and Switzerland designed to limit suicides among soldiers by reducing gun access have seen significant results among the target population.
States with stricter gun laws in the US, particularly Permit-to-Purchase laws, see significantly lower rates of overall suicide, with little evidence of a substitution effect from firearms to other means.
Australia’s gun buyback and suite of other reforms in 1996 resulted in a significant reduction in suicides according to multiple studies.
While evidence demonstrating the causal relationship between gun ownership and suicide is incontrovertible, there is more ambiguity about the extent to which gun laws can attenuate this problem. Part of the challenge is that many gun laws do not affect firearms that are already in the household (gun buyback programs, mandatory locks, and domestic violence policies that remove firearms from abusers are several exceptions), and will therefore only have an effect on suicides in populations previously unexposed to firearms. Further, most firearm laws are passed with reducing homicide and/or crime in mind, not suicides.
Nevertheless, a 2017 study evaluating this question found that states with both universal background checks and waiting periods saw statistically significant decreases in the suicide rate over the 2013-2014 time period, even after controlling for a host of relevant variables. States with both laws reported a decrease in suicide rates of 0.76 suicides per 100,000 persons, while states with neither law reported an increase of 1.04 per 100,000 persons. The same paper found no statistically significant effect of open carry legislation or gun lock legislation on the suicide rate.
Another study examined suicide rates in Connecticut and Missouri after both states changed their permit-to-purchase (PTP) handgun laws. In 1995, Connecticut passed a law requiring a permit and eight hours of gun safety training before acquiring a firearm. In 2007, Missouri repealed a 1921 law that required residents apply in-person with local police to purchase a gun. The paper found that Connecticut reduced suicides by 15% compared to what rates would have been in the absence of a PTP policy. Meanwhile, gun-related suicide rates in Missouri were 16% higher from 2007 to 2011 due to the repeal of its PTP policy.
One particularly influential paper examined the effects Australia’s 1996 gun law reforms. In the aftermath of the firearm massacre in Tasmania, which ended with the death of 35 people, Australia implemented the following reforms: a prohibition of rapid-fire long guns, a gun buyback program in which over 700,000 guns were removed from an adult population of 12 million, a prohibition of firearm sales by private vendors, and a legal requirement that all guns be registered to their licensed owners. The paper found that the rate of decrease in firearm suicides more than doubled from 3% per year to 7.4% per year after the implementation of Australia’s gun laws. Moreover, the paper found that there was no evidence of a “substitution effect” that is, would-be suicide victims were not substituting to other methods to commit suicide in the absence of guns. The paper found that total suicide (all methods including firearms) increased by an average of 1% per year before the introduction of the gun laws and decreased by an average of 4.4% per year after the introduction of the gun laws.