For years, New South Wales police have closely guarded a crucial detail about roadside drug testing: how much cannabis in a driver’s saliva is required to trigger a positive result.
The figure has remained largely undisclosed despite repeated questions about the sensitivity of roadside testing devices used to detect drugs such as delta-9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis.
But that secrecy has come under renewed scrutiny as the NSW government moves to introduce a legal threshold for drivers who use medicinal cannabis.
At a parliamentary budget estimates hearing on Friday, Roads Minister Jenny Aitchison told lawmakers that police had informed her that the roadside testing equipment was set to detect THC at 50 nanograms per millilitre (ng/ml).
The disclosure immediately raised questions about the accuracy and sensitivity of the roadside testing system, particularly because Australian and New Zealand standards prescribe a substantially lower 15 ng/ml cut-off concentration for cannabinoids in saliva drug tests.
The issue has become politically significant because the proposed reform would, for the first time, place the 50 ng/ml threshold directly into NSW legislation for registered medicinal cannabis patients.
Under the existing law, NSW operates what is commonly described as a zero-tolerance approach to drug driving.
Section 111 of the Road Transport Act makes it an offence to drive with the “presence” of an illicit drug in a person’s system, including THC.
The law does not currently distinguish between the amount of THC detected or whether the substance was legally prescribed as medicinal cannabis.
That has created a difficult situation for patients who may lawfully use cannabis as a medicine but still face penalties if THC is detected during roadside testing.
The proposed changes are intended to address part of that problem by establishing a threshold and introducing a warning system for registered medicinal cannabis users.
However, Friday’s hearing exposed questions about how the proposed legal limit relates to the equipment police actually use on roads.
The roadside testing device at the centre of the debate is the DrugWipe 3S, manufactured by German company Securetec.
Securetec’s website lists several DrugWipe models and states a THC detection limit of 5 ng/ml for its 5S and 6S devices.
NSW Police, however, have repeatedly declined to publicly confirm the detection limit of the 3S model used in the state.
The lack of transparency has become particularly contentious because roadside testing is the first stage of a process that can have immediate consequences for drivers.
At Friday’s hearing, Aitchison was asked about the figure and said police had told her that the device was set at 50 ng/ml.
“The DrugWipe is set at 50 [nanograms per millilitre],” she told the parliamentary committee.
The answer surprised Greens MLC Cate Faehrmann, who questioned whether the 50 ng/ml figure was correct.
Faehrmann suggested the roadside devices could be capable of detecting THC at much lower concentrations and said medicinal cannabis patients were confused about how the proposed system would operate.
“Did somebody mishear someone and put 50 in?” she asked.
“I’m trying to understand because medicinal cannabis patients are contacting me. They’re very confused.”
Aitchison, however, maintained that 50 ng/ml was the figure provided to her by police.
“What we’ve had in conversations with police is that 50 nanograms was the level set for roadside detection,” she said.
“It’s the same kind of test that’s been used for two decades.”
But the minister acknowledged that she did not know who had originally established the detection level.
“Who and what set those detection levels, I can’t tell you,” she said.
That uncertainty is now central to the political debate surrounding the proposed legislation.
The controversy stems partly from the difference between the legal wording of NSW’s drug-driving laws and the practical operation of roadside testing.
Under the existing legislation, the presence of an illicit drug such as THC can constitute an offence.
In theory, this means the law does not establish a minimum concentration at which THC becomes illegal.
In practice, however, police cannot detect every trace of a substance. Roadside testing equipment operates according to technical detection thresholds.
The distinction matters because the proposed medicinal cannabis reform would introduce a 50 ng/ml threshold for registered patients.
A patient with THC below that level would technically not breach the proposed threshold.
Yet if the roadside device is actually calibrated to detect THC at 50 ng/ml, a driver below the threshold would seemingly be unlikely to return a positive roadside result.
The hearing therefore raised a basic question: if the device reliably identifies THC at 50 ng/ml, why would a medicinal cannabis patient with a concentration below that level be detected during the roadside screening process?
The answer becomes more complicated because the roadside device may also detect lower concentrations.
Transport for NSW deputy secretary Sally Webb provided one of the clearest explanations of the current enforcement process during the hearing.
She compared the DrugWipe screening process to a COVID-19 test, which produces a positive or negative result rather than providing a precise measurement of the amount of substance present.
According to Webb, when a driver receives a positive roadside result, another DrugWipe test is conducted using a device from a different batch.
If the second test is also positive, the driver is suspended from driving for 24 hours.
That temporary suspension would also apply to registered medicinal cannabis patients under the proposed system.
Police then collect a saliva sample from the driver and send it to a laboratory for further analysis.
The sample is placed in an esky for transportation to the laboratory, where more sophisticated testing is conducted.
It is that laboratory result, rather than the roadside screening result alone, that ultimately determines whether a driver is prosecuted.
The hearing produced another significant figure.
Webb told the committee that the threshold used by the laboratory for laying charges is currently 10 ng/ml.
That is considerably lower than the 50 ng/ml figure given by Aitchison for roadside detection.
The distinction between the two thresholds is important.
The roadside DrugWipe is a screening device. Its purpose is to identify drivers who may have a prohibited drug in their system.
The laboratory test is used to establish whether the substance is present at a concentration sufficient for prosecution under the relevant legal framework.
According to Webb, the laboratory threshold for charging a driver is 10 ng/ml.
Under the proposed medicinal cannabis arrangements, however, a registered patient who had exhausted their two warnings would face prosecution once the THC concentration reached 50 ng/ml.
This creates two very different thresholds within the same enforcement process: one for roadside screening and another for laboratory analysis.
The proposed system would therefore give medicinal cannabis patients a degree of protection from prosecution, but not necessarily from the initial roadside consequences.
Webb also offered an important qualification to the minister’s statement about the DrugWipe’s 50 ng/ml setting.
The device is “guaranteed” to return a positive result at 50 ng/ml, she said, but it may also detect lower concentrations.
“It will at least detect 50, but it could detect 45, 40,” Webb said.
That admission adds another layer of uncertainty for medicinal cannabis users.
If the device can detect THC below 50 ng/ml, a registered patient could potentially return a positive roadside result even if their laboratory concentration ultimately falls below the proposed legal threshold.
Such a result could lead to an immediate 24-hour driving suspension while the sample is sent for laboratory testing.
The driver may later avoid prosecution if the laboratory result is below the applicable threshold, but the initial disruption would already have occurred.
For patients who depend on driving to work, attend medical appointments, care for family members or carry out everyday activities, even a temporary suspension could have significant consequences.
The debate has also highlighted the gap between the figure disclosed by the NSW government and the detection levels specified in Australian and New Zealand standards.
Those standards prescribe a 15 ng/ml cut-off concentration for cannabinoids in saliva drug testing.
New Zealand publicly states that its roadside screening threshold for THC is 15 ng/ml.
New Zealand Police also use the DrugWipe 3S, although the agency says its version of the equipment was specifically made for New Zealand and is not used in other jurisdictions.
That distinction makes direct comparisons difficult.
Nevertheless, the fact that the same model designation is associated with a publicly disclosed 15 ng/ml threshold in New Zealand has intensified questions in NSW about exactly how the devices used by NSW Police are configured.
The NSW Police response to questions about the equipment has been to direct inquiries to the manufacturer.
A police spokesperson reiterated the fundamental legal position.
“Driving with the presence of an illicit substance is an offence,” the spokesperson said.
But that answer does not resolve the technical questions raised at the estimates hearing about detection thresholds, calibration and the relationship between roadside screening and laboratory testing.
The proposed Labor legislation is designed to provide registered medicinal cannabis patients with greater protection than they currently receive.
The bill has already passed the NSW lower house and is now progressing through the Legislative Council.
Under the proposed arrangement, registered medicinal cannabis patients would receive two warnings over a two-year period if they were caught exceeding the prescribed THC limit while driving.
A third offence would trigger the full penalties under the law, including a minimum three-month licence suspension.
The reform therefore stops short of completely legalising driving after medicinal cannabis use.
Instead, it creates a graduated enforcement system intended to distinguish lawful medicinal use from repeated driving with elevated levels of THC.
Supporters of reform argue that the existing zero-tolerance framework fails to account for the growing number of Australians who use cannabis legally under medical supervision.
THC can remain detectable in the body after its impairing effects have diminished, meaning a positive test does not necessarily establish that a driver was impaired at the time they were stopped.
This distinction between impairment and presence has long been one of the central criticisms of Australia’s drug-driving regimes.
Road safety authorities, meanwhile, maintain that drivers affected by drugs pose a danger to themselves and others and that roadside testing is an important enforcement tool.
The parliamentary hearing has now placed the technical operation of NSW’s roadside drug-testing program firmly under scrutiny.
The most immediate question is whether the 50 ng/ml figure is an accurate description of the actual DrugWipe 3S threshold used by police.
The minister said police had given her that figure.
Transport for NSW subsequently explained that the device is guaranteed to detect THC at that level but may also produce positive results at lower concentrations.
Neither explanation provides a precise answer about the concentration at which the test will consistently produce a positive result.
That distinction matters because the proposed legislation is built around a specific 50 ng/ml threshold.
If roadside tests can detect concentrations significantly below that figure, medicinal cannabis patients could still find themselves caught in the screening process even when they have not exceeded the legal threshold that would ultimately determine prosecution.
The situation also highlights the difference between a screening test and a laboratory test.
A roadside device provides an initial indication. A laboratory analysis provides the evidence used for prosecution.
Between those two stages, however, a driver can face an immediate 24-hour suspension.
The controversy is unlikely to end with Friday’s estimates hearing.
Police Minister Yasmin Catley is scheduled to appear before the committee, where she is expected to face questions about the drug-driving reforms and the operation of roadside testing.
Among the issues likely to attract attention are the origin of the 50 ng/ml figure, the calibration of DrugWipe devices used in NSW, their actual sensitivity below the stated threshold, and the relationship between roadside screening and the 10 ng/ml laboratory charging threshold.
The debate also raises a broader question about how drug-driving laws should balance road safety with the rights of people legally using medicinal cannabis.
For NSW, the proposed reform represents a significant departure from the state’s traditional zero-tolerance approach.
But the disclosure of the 50 ng/ml roadside figure has also exposed a potentially confusing gap between legislation, police testing procedures and laboratory analysis.
Until authorities provide clearer information about how the devices are calibrated and what concentrations they can reliably detect, medicinal cannabis patients may remain uncertain about what the new rules will mean when they get behind the wheel.
