Mental Illness and Mass Shootings

We hear common questions about mental illness whenever a mass shooting occurs. Was mental illness to blame for the perpetrator’s actions? Would improving mental health treatment in the U.S. help prevent future shootings?  These questions are often raised by the U.S. public, journalists, and policymakers in the aftermath of events like the recent mass shootings in El Paso and Dayton. Many people assume the answer to these questions is “yes” – after all, how could anything except mental illness lead someone to commit such a horrific act? However, the research evidence tells a different story.

Mental illness is associated with a small but statistically significant risk of interpersonal violence. However, most people with mental illness are never violent: data from the National Epidemiologic Survey on Alcohol and Related Conditions shows that the 12-month prevalence of interpersonal violence in U.S. adults is about .8% among people with no mental illness, 1.7% among people with any mental illness, and 2.9% among people with serious mental illness, a category that includes people for whom the symptoms of mental illness cause significant impairment.  Further, the evidence shows that only 4% of all interpersonal violence in the U.S., including but not limited to gun violence, is attributable to mental illness – about 96% of all firearm homicides in the U.S. are caused by factors other than mental illness. In other words, if everyone with mental illness in the U.S. got 100% effective treatment, we could expect rates of firearm homicide to decrease by about 4%.

Anger, impulsivity, problematic alcohol use, traumatic life events, and a history of dangerous behaviors – for example, perpetration of domestic violence – are much stronger risk factors for interpersonal violence than mental illness. Mental illness is, however, an important risk factor for suicide, which accounts the majority of firearm deaths in the U.S.

Importantly, the statistics above are all based on studies of interpersonal violence writ large, not mass shootings specifically. High-quality research quantifying the relationship between mental illness and mass shootings is not available because of the statistically rare nature of such events. There are some prominent examples of mass shootings in which psychotic symptoms have played a documented role. For example, the 2011 shooting at then-U.S. Representative Gabrielle Giffords’ community forum in Tucson was perpetrated by an individual with undiagnosed and untreated schizophrenia whose psychotic symptoms directly contributed to his violent actions. However, the evidence clearly suggests that many mass shootings, as with other types of gun violence, are driven by factors, like those noted above, which have stronger and more direct links to interpersonal violence than mental illness.

From a policy perspective, the key take-home point from this evidence is that we cannot expect improvements to the U.S. mental health treatment system to solve our firearm homicide or mass shooting problems (though such improvements would certainly benefit the millions of Americans with mental illness).

Policies restricting access to firearms by high risk individuals have a much stronger evidence base. For mass shootings, state extreme risk protection order laws, which allow family members and law enforcement to petition the court for temporary removal of firearms from someone exhibiting dangerous behavior (also sometimes called ‘red flag’ laws) and restrictions on the assault-style weapons and large-capacity ammunition magazines disproportionally used in high casualty mass shootings, are evidence-informed options.

Better accountability for firearm sales through purchaser licensing, high standards for civilian gun carrying, and safe gun storage are three strategies that can help reduce the everyday occurrence of firearm homicide and suicide.

For suggestions on how to talk with your patients about firearm safety, please read “The 5A’s of Firearm Safety Counseling.”