Less than 2,000 motorists were tested for drug-driving since the legislation was introduced in April 2017, new figures show.
This compares to almost half a million breath tests for alcohol over the same period.
There were initially plans to carry out 50,000 drug-driving tests a year.
The figures, which were obtained by Independents 4 Change TD Tommy Broughan, show the number of alcohol and drug tests carried out on drivers at 101,965 garda checkpoints across the country.
1,939 drug-driving tests were carried out, compared with 472,165 breath tests for alcohol.
All three garda divisions in Cork have the most checkpoints: Cork North (9,681), Cork West (8,647), and Cork City (8,855).
The fewest checkpoints are in THE Dublin Metropolitan RegionS (DMR) South Central (704), North (712), and North Central (714).
Gardaí in Louth carried out the least number of drug-driving tests, performing just 3.
Four roadside drug-driving tests were carried out in Cork City over the past 18 months, compared with almost 24,000 breath tests for alcohol over the same period.
Other divisions where there were low testing figures were Wicklow (9), Donegal (11), Mayo (12), and Westmeath (14).
In Kildare, 268 drug-driving tests were carried out, the highest number recorded across the 28 garda divisions.
This was followed by Clare with 177 tests, DMR West (154), DMR East (152), and Cork West (124).
Kildare also had the highest number of breath tests, twice as many as any other division, with more than 44,000.
This was followed by Laois/Offaly (more than 29,000), Galway (more than 28,000) and Clare (25,000).
Sligo/Leitrim carried out the least amount of alcohol tests on motorists (8,000), followed by DMR North Central (almost 8,700), Kilkenny/Carlow (9,500) and Westmeath (9,700).
Meanwhile, drivers are being reminded today to reduce their speed or else face prosecution.
'National Slow Down Day' is underway until 7am tomorrow morning, with gardai out in force in a bid to clamp down on those speeding.
157 people died on our country's roads last year, with one in three involving speed.