Figures released to the Otago Daily Times under the Official Information Act showed 575 motorists had been charged with drug-driving between the introduction of new legislation on November 1, 2009 and July this year.
During the same period, a further 134 motorists were charged under older legislation.
National Manager Road Policing Superintendent Carey Griffiths said numbers charged with drug-driving were far lower than for drink-driving.
Police lacked a quick and accurate roadside test for drugs as was available for alcohol.
Supt Griffiths said the intention of current legislation was to remove impaired drivers from the country's roads, and police did not also test for drugs if a driver was found to be under the influence of alcohol.
"The vast majority of impaired drivers are impaired by alcohol."
In November 2009 amendments to legislation allowed police to require a compulsory impairment test to be completed, and to take blood samples for drug analysis.
Asked why Bay of Plenty had almost double the number of drug-driving charges as the next highest district, Supt Griffiths said numbers were too small to ascertain the reason.
The Bay of Plenty recorded 128 drug-driving clearances under the amended legislation, and a further 10 under the old legislation. Northland was the next highest with 65 and eight charges, respectively.
Southern District police recorded the highest number of drugged drivers in the South Island, charging 44 motorists - and a further 16 under the old system.
Southern District road policing manager Inspector Andrew Burns said "our focus is on removing people who are intoxicated [either as a result of alcohol or other substances] from our roads".
When police identified motorists who were intoxicated, by alcohol or another substance, they tested first for alcohol with an evidential breath test, he said.
At any point when police reached the conclusion someone was potentially affected by drugs other than alcohol, they administered the compulsory impairment test.
Cannabis was the drug of choice in the Southern District and was the drug most often detected in drugged drivers in the district.
