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Does Psychosis Play a Role in Most Mass Shootings?

New research rules out mental illness as a major factor in mass shootings.

Key points

  • Mental illness—specifically psychosis—is not a key factor in most mass shootings, new research finds.
  • Fixating on mental illness alone will do little to address this spiraling death toll from mass shootings.
  • Universal background checks and "red flag" laws identifying people who are potential mass shooting risks would be more effective, experts argue.

Even as we reel from yet another school shooting, this time leading to the death of 21 people at an elementary school in Uvalde, Texas (and with many more since), we are still faced with the same inevitable question of how such shootings can be prevented in the future.

To counter calls for stricter gun control, many newspapers and politicians have instead placed the blame for the Uvalde shooting on the presumed mental illness of the shooter in question, much as they have in previous shootings. For example, following the 31 deaths resulting from mass shootings in Dayton, Ohio, and El Paso, Texas in August of 2019, then-President Trump publicly stated that "mental illness and hatred pulled the trigger, not the gun." He also called for broader institutionalization of people with mental illness to prevent more shootings, regardless of any actual indication of violent behavior.

But even as budgetary concerns are leading to major cutbacks in mental health funding across the United States and elsewhere, media speculations linking mental illness with violence adversely affect how people with serious mental illness are treated. While studies consistently show that the mentally ill are far more likely to be victims of violent crime than vice versa, mass shootings such as the one in Uvalde make treating mental illness far more difficult as a result.

To help challenge beliefs about mental illness and mass shootings, a recent study published in the journal Psychology, Public Policy, and Law examined the mental health histories of 176 mass shooters since 1966. A team of researchers led by Jillian Petersen of Hamline University's Department of Criminal Justice used data taken from the Violence Project Database of Mass Shootings in the United States.

Funded by the National Institute of Justice, the Database focused on all mass shootings involving four or more victims between 1966 and 2020. This includes collecting nearly two hundred life-history variables on each shooter, including mental health history, trauma, situational triggers, and interest in previous shootings. The full database, including major findings and the methodology used, can be found at and makes for disturbing reading.

For the purpose of the current study, Dr. Petersen and her co-authors looked primarily at mental health variables, including the history of psychiatric hospitalization, medication, counseling, and the diagnoses received when such information was available. The researchers also looked at what motivated shooters, usually taken from public "manifestoes" as well as what was known about their life circumstances, criminogenic risk factors, and their access to guns. Those shooters who had been diagnosed with psychotic symptoms were examined to determine how strong the symptoms were and whether they played a role in the shooting.

The results showed that the actual role of psychosis in mass shootings has been relatively stable over time, even as the number of mass shootings has risen sharply in the past few years. All told, psychosis does not appear to have played a role in 69 percent of all shootings since 1966. When examined more closely, psychosis was deemed to have played a major role in 11 percent of shootings, a moderate role in 9 percent of cases, and only a minor role in 11 percent of cases.

These figures compare closely with most other research looking at violent crimes and the mentally ill. About the only real difference found appears to be that psychotic shooters tend to be more educated than non-psychotic mass shooters. Also, while approximately 60 percent of all mass shooters do have some mental health history, psychiatric medication usage was on par with what can be found in the general population.

There also doesn't appear to be any significant difference between mass shooters with psychosis and those without when looking at the type of firearms used and how they accessed those guns in the first place. When looking at firearms used, only 11.9 percent involved assault rifles, with the majority of mass shootings by people with psychosis involving handguns. Also, despite their history of mental illness, including being involuntarily hospitalized at times, most of these mass shooters successfully passed background checks and purchased firearms legally.

These results indicate that while mental illness is being blamed for the recent rise in mass shootings, psychosis alone doesn't appear to be a significant factor. To put it more succinctly, as the authors pointed out in their study, "dangerous weapons stay dangerous no matter who holds them." While there are limitations to this study since it focused exclusively on psychosis and used a fairly small sample, it seems clear that much of the current blame for mass shootings on mental illness by politicians and the media seems overblown.

Though not every perpetrator in a mass shooting has a clear motive (especially since many either die by suicide or are killed during the shooting), we usually know enough about the various motivations they give for their crimes to establish that mental illness is rarely a major factor. Whether due to a clear political agenda, a reaction to bullying or abuse, or simply in the hope of becoming notorious, those mass shooters who are arrested are rarely found not guilty by reason of insanity afterward.

Jillian Petersen and her co-authors argue that the most effective strategy for preventing mass shootings would be to curb access to assault rifles (the most commonly used weapon in such crimes) including more stringent safety checks on people seeking access to such guns. While the federal Gun Control Act of 1968 supposedly prohibits the sale to and possession of firearms by people who have been involuntarily committed to a treatment facility, many such people can still pass safety checks due to how the Act is enforced.

Experts also contend that better universal background checks and "red flag" laws identifying people who are potentially mass shooting risks should also be rigidly enforced nationwide. Improved mental health interventions are also vitally needed, including crisis intervention for people experiencing a mental health crisis. In much the same way they have proven effective in suicide prevention and domestic violence, they may help reduce mass shootings as well.

Though the entire issue of gun control remains a political minefield in U.S. politics, progress is still possible. But fixating on mental illness alone will likely do little to address this spiraling death toll.


Peterson, J. K., Densley, J. A., Knapp, K., Higgins, S., & Jensen, A. (2022). Psychosis and mass shootings: A systematic examination using publicly available data. Psychology, Public Policy, and Law, 28(2), 280–291.

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