Junior Transport Minister Noel Ahern said the Medical Bureau of Road Safety (MBRS) is currently studying the progress of trials being carried out in Australia and other countries.
He said it made no sense that roadside alcohol testing was mandatory for motorists across the state but drug testing was not.
Raising the issue, Fine Gael TD Michael Ring told the Dáil: “The time has come in this country when we must put a compulsory test in place for people driving under the influence of drugs.
“There are hundreds of people being killed every year by motorists taking drugs and they’re getting away with it.”
The MBRS currently routinely tests blood and urine samples for drugs if they test negative for alcohol.
Mr Ahern said extensive roadside drug testing trials were taking place in overseas countries.
“We must wait and see how they develop, but they are not at the stage yet where they are on a sound legal footing. The courts may be able to drive a coach and four through them.”
He added: “As soon as there is a reliable roadside test for drugs we will change the legislation to allow for its introduction.”
Labour TD Tommy Broughan cited an MBRS survey that found that one-in-three drivers who tested negative for alcohol tested positive for drugs.