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Last year, after police in Aurora, Colo., had placed Elijah McClain in a chokehold, then handcuffed him, paramedics injected him with a dose of ketamine, a powerful sedative. They said he “appeared to be” exhibiting signs of “excited delirium”; he subsequently went into cardiac arrest and died. Earlier this year, police officers in Tacoma, Wash., cited excited delirium in the case of another unarmed Black man, Manuel Ellis, who died in custody. And in Minneapolis, as Derek Chauvin knelt on George Floyd’s neck for the final moments of his life, a fellow police officer said, “I am concerned about excited delirium or whatever.” This may be part of Chauvin’s defense against murder charges.

Across the United States, police officers are routinely taught that excited delirium is a condition characterized by the abrupt onset of aggression and distress, typically accompanying drug abuse, often resulting in sudden death. One 2014 article from the FBI’s Law Enforcement Bulletin describes “excited delirium syndrome” as “a serious and potentially deadly medical condition involving psychotic behavior, elevated temperature, and an extreme fight-or-flight response by the nervous system.”

How often is excited delirium invoked? It’s unclear, but in Florida at least 53 deaths in police custody were attributed to it over the past 10 years. One study showed that 11% of sudden unexplained deaths in police custody in Maryland from 1990 to 2004 were attributed to excited delirium. The American College of Emergency Physicians published a controversial position paper in 2009 stating its consensus that excited delirium is a valid disease, associated with a significant risk of sudden death.

But excited delirium is pseudoscience. It’s not a concept recognized by the American Medical Association or the American Psychiatric Association. It isn’t a valid diagnosis; it’s a misappropriation of medical terminology, and it doesn’t justify police violence.

While delirium is a well-recognized diagnosis frequently seen and treated by neurologists and psychiatrists, excited delirium is not. Delirium is defined in the Diagnostic and Statistical Manual of Mental Disorders as an acute, fluctuating disturbance in attention and cognition, typically provoked by an underlying medical condition such as infection, drug intoxication, a medication’s adverse effects or organ failure. It can have “hyperactive” or “hypoactive” features, meaning that patients may be agitated or drowsy, or may move between these states. A typical case might be seen in an elderly man admitted to a hospital with a urinary tract infection, who over the course of a day or two becomes confused (e.g., unable to understand where he is or recognize family members) and starts sleeping throughout the day and getting agitated overnight. Delirium is not associated with sudden unexpected death.

Excited delirium, on the other hand, stems from an 1849 description by Luther V. Bell in the American Journal of Insanity. Bell looked at 40 patients admitted with “fever and delirium” to the psychiatric facility at McLean Hospital in Boston. Proponents of the excited delirium diagnosis refer back to Bell’s description as historical data, but the cases he studied did not involve deaths occurring in the span of minutes to hours, but rather two or three weeks after admission. While it is not possible to retrospectively diagnose these patients, it’s likely that many of them suffered from forms of infectious or autoimmune encephalitis.

Charles V. Wetli, a forensic pathologist, first used the phrase “excited delirium” in 1985 to explain a series of sudden deaths in cocaine users, occurring primarily in police custody. Wetli also used the term to describe the deaths of 32 Black women in Miami during the 1980s, proposing that a combination of cocaine use and sexual intercourse had led to their demise. He posited that, with chronic cocaine use, “the male of the species becomes psychotic and the female of the species dies in relation to sex,” stating, “My gut feeling is that this is a terminal event that follows chronic use of crack cocaine affecting the nerve receptors in the brain.” Later, however, police attributed the deaths to a serial killer, and evidence of asphyxia was found upon re-examination of the corpses.

Despite these shaky origins and the lack of grounding in medical science, this concept — of a febrile, agitated state often culminating in death — has persisted, advanced by law enforcement. The features of this purported condition, as listed by the American College of Emergency Physicians, betray its entanglement with law enforcement, including “bizarre behavior generating phone calls to police,” “failure to respond to police presence” and “continued struggle despite restraint.” Several analyses have found that the majority of deaths attributed to “excited delirium” are associated with the use of physical restraint. Some emergency-medicine doctors who are proponents of the diagnosis have been criticized for having conflicts of interest with the stun gun industry. And the manufacturer of Tasers has helped popularize this diagnosis to help attribute Taser-associated deaths to other possible causes.

The syndrome is disproportionately diagnosed among young Black men, highlighting the racist undertones of the reported clinical symptoms: having “superhuman strength” and being “impervious to pain.” It winds up being a convenient scapegoat cause of death after a violent confrontation. Or it becomes a justification for police aggression that may be unwarranted. There is reason to believe that it increases the risk of police encounters turning fatal. When officers are taught that traditional tactics such as “pepper spray, impact batons, joint lock maneuvers, punches and kicks” are “likely to be less effective” against suspects with excited delirium, as the American College of Emergency Physicians paper suggests, they may resort to more aggressive maneuvers, such as knee-to-neck chokeholds or hogtie restraints. According to a 2012 article published by the Force Science Institute, at one police training seminar in Illinois, a police veteran described excited delirium suspects’ “imperviousness to pain” and recommended responding with force that is “fast and overwhelming, with a vascular neck restraint possibly considered as part of the package.” The result can be a tragic paradox: an apparently terminal “condition” that can be treated only with the escalation of force, inevitably increasing the chances that it will be fatal.

The other justifications for this “diagnosis” also fail to pass scientific muster. Some proponents of excited delirium point to the accumulation of “heat shock protein 70” in the brains of affected individuals. But this is also seen in deaths associated with cocaine use and is not evidence of a unique diagnosis. Others cite cases of extreme responses to stimulant use and emotional duress, such as heart failure and cardiac arrest, but these cases are not associated with agitation or altered consciousness. At any rate, cardiac stress responses are much more common in older, postmenopausal women, not in younger Black men, who aren’t a particular risk for this kind of stress response but are disproportionately likely to be killed in police encounters.

Excited delirium implies that there is a medical condition that predisposes certain individuals, often Black men, to die in police custody. It draws upon aspects of real medical conditions such as delirium, psychosis, drug intoxication and sudden cardiac death. But it manipulates them to form a broadly applicable blanket diagnosis that serves the interests of law enforcement and absolves officers of accountability.

Méabh O’Hare is a neuromuscular fellow at Massachusetts General Hospital and Brigham and Women’s Hospital. Joshua Budhu is a neuro-oncology fellow at Massachusetts General Hospital, the Dana Farber Cancer Institute and Brigham and Women’s Hospital. Altaf Saadi is a general academic neurologist at Massachusetts General Hospital and an instructor of neurology at Harvard Medical School. They wrote this article for the Washington Post.