More than 700 drivers have been nabbed for drug-driving since a new law came into effect.
Figures released under the Official Information Act show 575 motorists were charged with drug-driving from when new legislation was introduced on November 1, 2009 to July this year.
During the same period, another 134 motorists were charged under older legislation.
The national manager of road policing, Superintendent Carey Griffiths, said the drug-driving numbers were far lower than for drink-driving.
"Police lacked a quick and accurate roadside test for drugs as there was with alcohol."
Mr Griffiths said the law's intention was to remove impaired drivers from roads, and if a driver was found to be under the influence of alcohol, police did not also test for drugs.
"The vast majority of impaired drivers are impaired by alcohol."
The Bay of Plenty recorded 128 drug-driving charges under the amended legislation and a further 10 under the old legislation. Northland was next highest with 65 and eight.