Tasers are increasingly being used by UK police yet recent studies suggest the health risks are greater than previously thought, reports The BMJ this week.
Of particular concern, is the frequent police use of Tasers against mentally ill patients, often within hospitals and care homes. This has prompted the UK home secretary, Theresa May, to order a review of police use of force against mentally distressed people.
Tasers are used by over 16,000 police forces in 107 countries, explains journalist Owen Dyer in a special report published today. The device uses compressed nitrogen to fire two barbed electrical probes that deliver a pulsed 50,000 volt shock, causing intense skeletal muscle contractions and pain.
The most commonly used Taser (the X26) also has a "drive-stun" mode, in which two electrodes at the front of the weapon are held against the body, causing pain but not muscle contractions. A pull of the trigger delivers five seconds of current, more if the trigger is held down.
In the United Kingdom, use of Tasers tripled between 2009 (when police officers not trained in firearms were first allowed to carry them) and 2013. Police drew tasers on 10,380 UK civilians aged 14-85 years in 2013 and fired them in 20% of those cases. A similar number of police officers received shocks while training.
Known health risks include eye injuries, seizures, collapsed lung (pneumothorax), skin burns, and muscle, joint, and tendon injuries. The most dangerous risk is head injury from uncontrolled falls, which has led to deaths.
But there is still much debate about whether Tasers affect the heart, in particular the potential to induce lasting heart rhythm problems (arrhythmias).
Most of the existing research is sponsored by the manufacturer so its neutrality has been questioned. But the UK ministry of defence's scientific advisory committee on the medical implications of less lethal weapons, warns that "it would be prudent to assume that a similar effect could be exerted by the Taser X26."
More recently, a study of eight cases concluded that Tasers had caused irregular heart rhythm (ventricular fibrillation). And a US National Institute of Justice review concluded that direct inducement of cardiac arrhythmias in "a confluence of unlikely circumstances" was a "plausible but unproven" outcome.
Contrary to statements on its website, Taser has already been found negligent by a court in one death for failing to warn officers of the dangers of discharging into the chest and giving lengthy shocks.
In the US, Darryl Turner, 17, who refused to leave a North Carolina supermarket after being made redundant, died of ventricular fibrillation shortly after he was "tasered" for 37 seconds.
In Britain a court has just attributed the first death to use of a Taser. Jordon Begley, a 23 year old factory worker, died from cardiac arrest two hours after Greater Manchester police used a Taser on him in 2013.
An inquest concluded in July that the nine second shock he received in conjunction with two "distraction strikes" - punches to the head from officers while handcuffing him - "more than materially contributed" to the stress that led to his cardiac arrest.