Police chiefs in England and Wales are considering whether to extend trials of high-voltage stun guns.
The gun is used as a less lethal alternative to conventional weapons
A 12-month pilot scheme in five police forces ended this weekend but a final decision has not been made on whether the guns will be used nationwide.
The Metropolitan Police Federation has strongly backed the use of "tasers".
But Amnesty International argues the guns, which are being used by forces including Lincolnshire Police, have not been properly tested.
The lobby group says several people in the US and Canada have died after being shot with the stun guns.
It has called for full medical trials to be carried out before the government allows the stun guns to be issued across the country.
Taser guns fire needle-tipped barbs up to eight metres to deliver a disabling, 50,000-volt shock.
They are considered a "less lethal" alternative to conventional firearms.
Apart from the Met, the other police forces taking part in the trials are Northamptonshire, Thames Valley, Lincolnshire and North Wales.
A report from the Association of Chief Police Officers (ACPO) in December 2003 revealed some officers had expressed concerns about the stun gun's reliability.
In three cases more than one discharge was required to subdue a suspect and on two of these occasions "Taser firings did not appear to go right the first time", it added.
But the stun gun was thought to have significant "deterrent effects" and "a number of operational benefits for police".
In June 2003 North Wales Police used a taser gun against a dangerous dog which was running amok in Wrexham.
The gun failed to floor the dog - one of the barbs became detached, breaking the circuit - and the animal ran off.