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."