The next most common drug was benzodiazepines.
Almost 2,500 people drove under the influence of cannabis last year.
The Medical Bureau of Road Safety will tell an Oireachtas committee today that nearly 1,400 tests detected cocaine in 2021.
The next most common drug was benzodiazepines, with the same substances the most prevalent again this year.
Transport commentator Conor Faughnan says the figures are the 'tip of the iceberg'.