Gardaí have been warned that their new roadside drug testing kits may not work when it is cold.
The Medical Bureau of Road Safety advised the traffic corps on "proper operating conditions for the analysers" and confirmed that the device is not guaranteed to work when below 5C.
Using saliva samples, the machines are designed to detect drivers high on illicit drugs such as cannabis, cocaine and heroin.
"At temperatures lower than 5C the analyser is capable of operating as it has the capacity to provide heat internally," the bureau said.
"Where the analyser cannot achieve 5C, a 'low temperature message' will be displayed and it will not be possible to do a test."
Eighty-six of the Drager DrugTest 5000 drug-screening devices - considered the best on the market - are being kept in Garda stations.
Another 50 are being used for roadside tests, with the number of these mobile kits to rise to 150.
The Road Safety Authority (RSA) confirmed that it was not aware of the temperature limitations of the device.
The DrugTest 5000 is widely used by police forces, including in Australia, Spain, Italy, England and Wales, and in Norway, where officers claim that in practice it can be used briefly outside in freezing temperatures if they stand beside a patrol car with the boot or doors open while analysing a sample.
Other advice from the Medical Bureau of Road Safety to Garda trainers about the devices states that the disposable tester should be discarded if its packaging is not intact or if dessicant is not present.
The top end of the operating range is 40C.
Independent TD Tommy Broughan, who has campaigned on road safety issues, said: "It would stop gardaí having a comprehensive checking regime.
"It's something that wouldn't have occurred to me and it's something of a serious concern.
"Clearly with our climate it could introduce a restriction."
Independent TD Clare Daly said it is "almost unbelievable" that any questions would emerge over new roadside testing kits while the Garda is facing questions over bogus drink-driving test records.
She said: "Who would decide to purchase equipment which cannot be relied upon for accuracy in temperatures below 5C?
"Accuracy of results is critical when we are dealing with serious allegations which result in penalties and higher premiums for motorists."
The results from the initial tests cannot be used in evidence in court.
But under the Road Traffic Act 2016, which came into force in mid-April, any driver stopped and asked for a sample at the roadside or at a checkpoint or following an accident faces the threat of a 5,000 euro fine or six months in jail for refusing to co-operate.
The results can also determine whether a driver is arrested on suspicion of driving while intoxicated and taken to a Garda station to give a blood or urine sample.
Each device including the carrier case costs 615 euro and each disposable tester costs about 15 euro.
The analysers can also identify the presence of several prescription drugs, causing concern for people on prescribed and heavy painkiller medication.
The Association of Garda Sergeants and Inspectors raised issues in the days after the test was introduced over the number of officers who had been trained to use the analysers.