Publication
Semple, T., Jenkins, B., Siamro, J., Brook, G., Dibayula, S., Bordeleau, E., Bussey, O., MacIsaac, A., & Bennell, C. (2025). Injuries and death proximate to conducted energy weapon use: A systematic review. Journal of Police and Criminal Psychology, 40, 816–831. https://doi.org/10.1007/s11896-025-09750-w
What Was the Issue?
Tasers have been a controversy magnet since officers first started carrying them. High-profile deaths during arrests have fed public skepticism, while agency adoption has kept climbing and inquests have kept recommending wider deployment. Two prior systematic reviews concluded CEWs were mostly safe, but both restricted themselves to high-rigor studies, which in this domain means healthy volunteers, medical screening, and controlled lab conditions. Out in the field, officers deploy CEWs on people who are often intoxicated, exhausted from struggle, and carrying pre-existing health conditions, the exact population the lab studies screen out. That mismatch left an open question. If you include everything published on CEW injuries between 2010 and 2021, including case reports and lower-quality field data, does the safety picture hold up?
How Did They Look at It?
The authors ran a systematic review, following a standard protocol that requires documenting every search and every decision to include or exclude a study so other researchers can check the work. They searched six databases using a wide vocabulary of CEW and harm terms, and they cast a broad net. Anything published or unpublished in English or French from 2010 forward counted if it touched on injuries or death proximate to a CEW deployment, with injury defined to cover physical, physiological, psychological, and cognitive harm. Literature reviews and opinion pieces were excluded, but case studies, internal police reports, and observational work were all in. Six coders screened everything independently and agreed with each other almost every time, then rated each study against a quality checklist the team built for this review.
The search returned 1,620 unique records, and 95 documents made the final pool. Most were US-based, and most looked at members of the public who had interacted with police. Physical injuries were the primary outcome in about 60% of them, with smaller groups examining physiological effects, deaths, and psychological effects.
Just under half of those documents were anecdotes, case studies, or internal non-peer-reviewed reports. Another three in ten were one-off measures with no comparison group. Randomized trials were rare. On the review's own quality checklist, only about a quarter of the studies controlled for potential confounding variables.
What Did They Find?
Across the three injury categories, the headline is that CEWs look generally safe, with the field's measurement practices muddying the rate estimates.
Psychological effects. Six lab studies examined psychological effects, all but one of them looking at cognitive impairment after a five-second exposure. Results were mixed, but the consistent pattern was that any measurable decrement in concentration, memory, or sobriety-test performance returned to baseline within an hour. The cognitive effect was comparable to a 100-yard sprint or a 30-second heavy-bag drill. The remaining study surveyed 100 officers exposed during training. Two-thirds reported extreme pain or motor problems, 13% reported panic or confusion, and a third had trouble processing what the instructor was saying while it was happening.
Physiological effects. Studies tracked blood chemistry, heart rhythm, blood pressure, and breathing. Some markers rose, but in nearly every case the researchers judged the changes medically insignificant, and most resolved within an hour. The one notable cardiac event in the lab literature was a single case where the device drove a subject's heart rate to 240 beats per minute, and it came from a pre-production unit that was later modified. Case reports added scattered instances of chest pain, heart attack, stroke, and muscle-tissue breakdown after field deployments, nearly all in people who had been struggling with officers, were intoxicated, or had other health problems in play.
Physical injuries. This is where the measurement problem shows up most clearly. Civilian injury rates across the studies ran from 0% to 57%, with an average around 14%.
Officer injury rates ran higher, averaging 24% and ranging from 0% to 45%. Those are officers hurt during the same field encounters, not officers taking exposures in training. The extremes have almost nothing to do with the weapon. They come from what each study decided to count. The study reporting zero logged only significant injuries across 504 deployments. The one reporting 57% counted probe punctures and had just 14 deployments in the denominator. Two more estimates in the forties also counted punctures. One agency, the New Zealand Police, reported year after year under the same regime. Across those years civilian injuries ran 6% to 15% and officer injuries 25% to 45%.
When injuries did occur, the majority were minor, mostly scrapes, bruises, and puncture wounds from the probes. Several studies found CEWs were associated with fewer civilian injuries than other force options. One found civilian injuries about six times less likely when a CEW was the only force used, with officer injuries nearly seven times less likely. Another, comparing agencies that allowed CEWs against agencies that did not, found 44% lower odds of severe civilian injury where they were permitted. One study ran the other direction and found CEWs increased civilian injury, but that result is driven by counting probe punctures.
Serious injuries did show up, just rarely. Among subjects, the case reports include severe nerve damage from three shocks to the base of the neck, probes embedded in the face or skull, two cases where a probe penetrated the brain, and several eye strikes that cost the subject vision or required surgery.
Two of the fracture cases came out of training rather than the field. One officer taking an exposure while lying on a mat fractured a shoulder blade. Another, taking one standing upright, sustained compression fractures in the spine. Both came from the involuntary muscle contraction itself.
Deaths. The fatality literature was almost entirely case reports and large reviews of media or medical examiner records. Six themes ran through the deaths. They were cardiac concerns, substance use, excited delirium syndrome (ExDS), head trauma from falls, burns, and positional asphyxia. The vast majority of decedents were male, ages 16 to 68, and most cases involved several of those factors at once.
Where researchers tried to assign cause, the CEW came out as a small share. One review of 175 fatalities judged 12% directly attributable to the deployment. Another, working from 213 medical examiner reports, listed the CEW as the cause of death in 1% of cases and a contributing factor in another 7.5%. In both, heart disease, drugs, and ExDS accounted for far more. A worldwide database of 1,030 fatalities yielded 16 deaths from head trauma after a forced fall, about 1.6%, and six deaths from burns where the CEW ignited fuel vapor or fuel-soaked clothing.
The causality picture is contested. One team applied a standard causality method to twelve cardiac-arrest cases originally attributed to CEW use and scored all twelve as unlikely to have been caused by the weapon. The researcher who had compiled the original cases pushed back, pointing out that the medical examiners themselves had disagreed on some of those same cases. Deaths happen. The field has no clean way to separate the CEW's contribution from intoxication, struggle, and existing heart disease.
So What?
The authors land on five main implications.
First, the substantial variability in injury rates across jurisdictions is largely an artifact of how studies define an injury. Future research has to report the operational definition clearly, and ideally separate probe puncture wounds from other injuries, so cross-jurisdictional and cross-weapon comparisons mean something.
Second, the brief cognitive impairment following CEW exposure has practical implications for officers. If de-escalation depends on verbal communication and the subject just took a CEW exposure, the officer should expect compromised processing in the first hour and adjust to simple, direct language. The authors flag this as relevant to ongoing de-escalation training discussions.
Third, post-incident medical evaluation should be mandatory for everyone subjected to a CEW. The case literature shows that the serious adverse events tend to surface when underlying conditions (cardiac disease, intoxication, ExDS) intersect with the deployment, and a medical look catches what officers cannot see at the scene.
Fourth, independent review of every CEW-proximate death is warranted. The cause of these deaths can be contested, and the authors argue an independent body is needed for credible answers and public trust.
Fifth, North American policing needs a national, uniform CEW adverse-event database. Without consensus definitions, sufficient context per incident, and consistent reporting, the field cannot identify the conditions that drive serious injury and death, and cannot mitigate them through training or policy.
The authors are direct about their limitations. The methodological quality of the included literature is poor, and use-of-force reports rely on officer perception of injury, which understates injuries that surface after the encounter. Some of the better-quality field studies were conducted by researchers affiliated with Axon, the largest CEW manufacturer, a conflict that future work should reduce by using independent investigators or blinded analysis. And the fatality reviews almost certainly double-count some deaths across studies because the case-level detail is too thin to deduplicate.
Their bottom line is that the CEW is a generally safe intervention option that probably reduces injuries to both officers and civilians compared to alternatives. Serious injuries and deaths do happen, infrequently, and the next decade of research has to do better at characterizing when and why.
My $.02
My read is that CEWs are generally safe.
But every use of force carries risk. Strange things and bad outcomes can occur even at the lowest levels of force. There is always a chance that someone can die when force is used. Holding a standard of zero bad outcomes is simply unreasonable.
This review shows that. CEWs generally appear to produce better injury outcomes than many other forms of force, but bad outcomes (including death) can still occur. The review suggests that most of these deaths involved intoxication, cardiac disease, or a prolonged struggle. This is the reality of police work. Officers don't get to choose whether they are dealing with someone who is intoxicated, in poor health, or simply is not going to give up. They must deal with what is presented to them.
I hope that future Taser studies will use more comprehensive coding schemes that allow a better understanding of Taser usage and injury. For starters, if probe punctures are counted as injury, they should be separated from other types of injury (except in the severe cases like skull penetration and eye hits mentioned above). Bundling injury that is expected to occur from successful use with other injuries does not allow us to see what is really occurring. It is also useful to know whether the probes were fired or a drive stun mode was used. Simply pulling the Taser or arcing it should be considered separately from actually attempting to stun someone.
Researchers can fix this in the next round of studies. Agencies can fix it sooner. Separating punctures from other injuries, and recording whether probes were fired, is a reporting change rather than a research project. Some agencies have already made it.