Almost 1,500 people tested positive for drug driving last year, it has been disclosed.
UCD professor Denis Cusack, director of the Medical Bureau of Road Safety, said gardai would be trained from early next year in how to spot drivers under the influence of drugs.
And he warned prescription medicines, and not just illegal drugs, could also cause a motorist to drive dangerously.
"If any one of us has a loved one killed by a driver who's impaired, quite frankly it doesn't really matter whether it is an 18-year-old out of his head on speed or a granny completely doped up on medications," he said.
"The end result is a death or an injury, and we have to be very cognisant of that."
At an international lecture on drug driving, hosted by the Road Safety Authority to mark Irish Road Safety Week, Prof Cusack said 5,355 blood and urine samples were passed to gardai last year, with 1,945 found to be under the legal alcohol limit.
But when the 1,945, plus another 35 samples, were examined further, 73% proved positive for drugs.
Prof Cusack said 831 people were prosecuted for drug driving last year, compared with 106 in 2005.