Mass Shootings’ Relationship to Mental Illness

Psychiatric TimesVol 41, Issue 2

If all violence in the US that is due to mental disorders could be eliminated, 95% to 97% of violent behavior would remain.

mass shooting



Nearly a year since our cover story “Changing the Narrative: Mental Illness and Gun Violence,” mass shootings in the United States have continued to dominate the headlines. Publishing its annual report on December 31, 2023, The Trace concluded that 2023 had the second-highest number of mass shootings on record, with 709 individuals killed and at least 2676 injured.1 The nonprofit research group Gun Violence Archive (GVA) defines a mass shooting as “4 or more shot or killed, not including the shooter.” GVA recorded 656 mass shootings in 2023. This is the second-highest number of mass shootings on record, slightly less than the 689 mass shootings in 2021 and slightly more than the 646 mass shootings in 2022.2

The mass shooting in Lewiston, Maine, on October 25, 2023, for example, left 18 dead and 13 injured and has once again brought to national attention the question of what can be done to prevent or minimize future mass shootings. In this instance, based on information reported by the media, it appears that the shooter experienced psychotic symptoms at the time of the shootings and reportedly had been psychiatrically hospitalized for 14 days in July while serving in the US Army Reserve.3 Predictably, these reports inflamed a long-held cultural narrative that mass shooters all suffer from mental illness and hence individuals with mental illnesses should not have access to guns. Objectively and consistently, experts on this topic from the fields of both psychiatry and criminal justice dispute this narrative and share a cautionary note that banning firearms among individuals with serious mental illness will do little to decrease mass shootings.4 Furthermore, policies targeting individuals with mental illnesses will likely impede individuals in psychological distress from seeking professional help due to their fear of being stigmatized and prevented from owning a firearm.

In response to our April 2023 cover story, we received correspondence from psychiatrists Nina E. Cerfolio, MD, and Ira D. Glick, MD, who have published articles in the psychiatric literature hypothesizing that most mass shooters in the US suffer from undiagnosed and untreated psychiatric illness. I read 2 of their publications relevant to the association between mass shooters and mental illness5,6 and was befuddled by their conclusion, especially in the context of the small number of mass shooters that they assessed—a total of 35 mass shooters over a 37-year period. On December 5, 2023, a summary commentary of these articles by Cerfolio and Glick appeared as the lead online article in a popular psychiatric publication, which restated their research and findings.7

They concluded that “Out of the 32 surviving assailants for whom we have sufficient evidence, 87.5% of perpetrators of mass shootings were diagnosed with major psychiatric illness, and none were treated appropriately with medication at the time of the crime.” Regardless of the authors’ intent, it is easy to see how this single sentence could become a rallying cry for politicians and activists to scapegoat individuals with a mental illness as the cause of and solution to mass shootings. In fact, gun laws against individuals with mental illness would not impact the potential mass shooters with undiagnosed and/or untreated mental illness, as they will not have been in the registry. Rather, these gun laws would likely decrease trust, honesty, and treatment entrance for those feeling violent.

The GVA reported that in 2022 there were 44,313 gun violence deaths in the United States, 20,223 of which were due to homicide, murder, accidents, or defensive gun use, and 24,090 deaths were due to suicide.8 Significantly, 647 of the nonsuicide deaths resulted from mass shootings. These numbers for a single year are staggering and in sharp contrast to the 35 mass shooters over 37 years that were intensively studied by Cerfolio and Glick. Using a standardized interview developed by the authors with DSM-5 criteria and the Mini International Neuropsychiatric Interview standardized scale, they reviewed court medical and psychiatric records. The 35 mass shooters studied included every case reported in the Mother Jones database of 115 mass shootings between the years 1982 and 2019 who survived the mass shooting and entered into criminal proceedings.9 It is important to note that this is a highly enriched subset of the typical mass shooter—the majority die during or shortly after the event.

Meanwhile, research highlights the lack of evidence pointing to mental illness as the main reason for mass shootings. Following the mass shooting in Newtown, Connecticut, in December 2012, Appelbaum wrote a commentary in which he states, “First, much of the increased risk [of violent behavior] seen in people with mental disorder is attributable to other variables rather than to the disorders themselves.”10 Additionally, he cites US data that attribute 3% to 5% of violence in the US to mental disorders. Hence, if all violence in the US that is due to mental disorders could be eliminated, 95% to 97% of violent behavior would remain.

Knoll and Annas report in their highly referenced chapter titled “Mass Shootings and Mental Illness” that common attributes among individuals who commit mass murder include feeling socially alienated, extreme feelings of anger and revenge, planning the shooting well in advance, paranoid traits, and a lack of intent to survive the event (with the plan of suicide or the expectation to being killed by law enforcement).11 They conclude the following:

“In sum, the extant research on mass murders suggests that these events are caused by a complex interaction of emotional turmoil, psychopathology, traumatic life events, and other precipitating factors unique to each case.”

Throughout the literature that I reviewed, substance abuse is a more common factor associated with violence by individuals with and without mental illness. Fazel et al concluded12:

“Schizophrenia and other psychoses are associated with violence and violent offending, particularly homicide. However, most of the excess risk appears to be mediated by substance abuse comorbidity. The risk in these patients with comorbidity is similar to that for substance abuse without psychosis.”

There is agreement that serious mental illness does contribute to a subset of mass shootings, with a commonly referenced estimate of 20%, or 1 in 5 mass shootings. Although improving the diagnosis and treatment of mental illnesses should always be part of the conversation, there is a paucity of information about the 80% of mass shootings that are not a direct result of a mental illness. Notably, a joint consensus of 60 mental health organizations in June 2022, including the American Psychiatric Association, stated13:

“Attempts to connect mental illness to mass shootings are a distraction that inflicts enormous damage by taking attention from solutions that could actually prevent such events. This perpetuates a false narrative that encourages stigmatization of and discrimination against the millions of Americans living with mental health conditions.”

Sadly, when the year-by-year numbers of death by gun violence are reviewed, over 50% of these deaths are by suicide, not homicide, and there is a large percentage of acute mental illness at the time of these deaths.14 From a public health perspective, increased education on suicide prevention, increased screening for suicide risk, and increased awareness of the need to secure all firearms to create a barrier to impulsive access should be areas of high priority.

As we settle into 2024, a public health issue that should be at the top of our national agenda is what steps we can take to decrease the growing number of mass shootings in the United States. As a psychiatrist, I am concerned about a common cultural narrative that blames all mass shootings on individuals suffering from a serious mental illness. Human nature seems to seek a simple and direct causation for most emotionally troubling and confusing events, as this provides an illusion of control, decreases the feelings of helplessness, and allows a cognitive closure to the event that is commonly rooted in wide-ranging social, political, and cultural factors. Many potential interventions and policy changes exist and have been debated with strong emotions on both sides of the political spectrum but with no tangible results to address this steadily growing national crises. The first step in creating a cooperative dialogue on any controversial topic is to establish the evidence as it exists at the present time.

Clearly, much more research is needed to continue to unravel the complexities of factors that ultimately converge to motivate an individual to commit a mass shooting. Ideally, a thorough clinical assessment immediately prior to and just after a mass shooting by a surviving shooter would be available, albeit unlikely in most cases. Finally, if a mass shooter has been diagnosed with a serious mental illness—treated or untreated—this does not necessarily translate into causality. A mass shooting by an individual with a serious mental illness could have been motivated by a wide range of emotions and/or stressors that can be experienced by us all. It also would have included additional factors that synergized to cross that line to devastating action—factors that can be independent of the serious mental illness.

Dr Miller is Medical Director, Brain Health, Exeter, New Hampshire; Editor in Chief, Psychiatric Times; Staff Psychiatrist, Seacoast Mental Health Center, Exeter; Consulting Psychiatrist, Exeter Hospital, Exeter; Consulting Psychiatrist, Insight Meditation Society, Barre, Massachusetts.


1. Brownlee C. Gun violence by the numbers in 2023. The Trace. December 31, 2023. Accessed January 8, 2024.

2. Gun Violence Archive. Accessed January 8, 2024.

3. Berman M, Slater J, Wax-Thibodeaux E. Why all the warnings about the Maine gunman didn’t stop the massacre. Washington Post. November 2, 2023. Accessed January 8, 2024.

4. Skeem J, Mulvey E. What role does serious mental illness play in mass shootings, and how should we address it? Criminol Public Policy. 2020;19(1):85-108.

5. Glick ID, Cerfolio NE, Kamis D, Laurence M. Domestic terrorist and mass shooters: Prevalence of untreated psychiatric illness. J Clin Psychopharmacol. 2021;41(4):366-369.

6. Cerfolio NE, Glick ID, Kamis D, Laurence M. A retrospective observational study of psychosocial determinants and psychiatric diagnoses of mass shooters in the United States. Psychodyn Psychiatry. 2022;50(3):513-528.

7. Cerfolio NE, Glick ID. Mass shooters and mental illness: reexamining the connection. Clinical Psychiatry News. December 5, 2023. Accessed January 8, 2024.

8. Past summary ledgers: archive 2022. Gun Violence Archive. March 2, 2023. Accessed January 8, 2024.

9. Follman M, Aronsen G, Pan D. A guide to mass shootings in America. Mother Jones. Updated December 6, 2023. Accessed January 5, 2024.

10. Appelbaum PS. Public safety, mental disorders, and guns. JAMA Psychiatry. 2013;70(6):565-566.

11. Knoll JL, Annas GD. Mass shootings and mental illness. In: Gold LH, Simon RI, eds. Gun Violence and Mental Illness. American Psychiatric Association; 2016:81-104.

12. Fazel S, Gulati G, Linsell L, et al. Schizophrenia and violence: systematic review and meta-analysis. PLoS Med. 2009;6(8):e1000120.

13. Statement on gun violence crisis from 60 national organizations. American Academy of Child and Adolescent Psychiatry. June 6, 2022. Accessed January 8, 2024.

14. Baumann ML, Teasdale B. Severe mental illness and firearm access: is violence really the danger? Int J Law Psychiatry. 2018;56:44-49.

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