From twisted testicles to babies electrocuted in the womb, Tasers are presenting emergency departments with unprecedented injuries, a paper by a New Zealand doctor shows.

Tasers, which are being introduced into New Zealand and Australian police forces as an alternative to firearms, paralyse a person by delivering electrical pulses through metal barbs shot from a gun.

Former Wellington doctor Megan Robb, an emergency medicine registrar at Townsville Hospital in Queensland, led a review of 86 international medical studies on Tasers, dealing with heart and respiratory problems, drugs, alcohol, pregnancy and trauma.

The article, published in the journal of the Australasian College for Emergency Medicine, highlights several cases, including:

- A psychiatric patient who removed the barb from his skin and swallowed it.

- A pregnant woman who miscarried after a barb lodged in her abdomen.

- A 16-year-old boy whose skull was penetrated by the dart.

- A man whose lung was punctured after being shot in the chest.

- Two police officers who suffered compression fractures in their spines from muscle spasms.

- A man who developed a twisted testicle.

Australian police were criticised last week when glue-sniffer Ronald Mitchell, 36, caught fire and suffered third-degree burns to 10 per cent of his body when he was Tasered. He had been charging at police with a can of petrol and a cigarette lighter.

A 2006 study by Amnesty International found Tasers were implicated in more than 150 deaths.

However, Dr Robb and her colleagues found that, despite Tasers being used extensively for decades, there was limited research into their implications for those most likely to be shot, such as the mentally ill, those under the influence of drugs and violent offenders.

"The Taser is not likely to be used on normal, healthy resting adults, where much of the research has been performed."

Emergency departments could expect to see more patients who had been Tasered, and it was important for doctors to be aware of those at higher risk of complications, Dr Robb said.

After a year-long trial, Tasers were introduced fully in Auckland and Wellington in December and are being introduced nationwide.

Since December, Tasers have been presented at people 33 times and fired five times. This month, the threat of a Taser was enough for a branch-wielding man to give himself up to police on the banks of the Waikato River.

Superintendent John Rivers said more than 60 per cent of cases requiring the use of force involved people believed to be affected by alcohol or drugs and 13 per cent involved people having "some kind of mental health crisis".

"Our preferred tactical option is always communication, but when you have drugs or alcohol involved, the likelihood is that the effectiveness of communication as a tactical option will be diminished."

Police Association spokesman Chris Cahill said that, although people under the influence of drugs, alcohol or stress were at higher risk from Tasers, those same people were also most likely to die from being physically restrained or shot.

"Our Australian comrades tell us that, nine times out of 10, just the threat [of a Taser] is enough to calm people down. Once they see the red light on them, they stop."