Can you stand on one leg with your eyes closed?
That was one of the tests suggested to a New South Wales parliamentary inquiry in Sydney as a way of deciding if a motorist was fit to drive after using medicinal cannabis.
The inquiry heard from a range of experts about a Greens bill designed to protect medical cannabis patients in NSW from drug-driving charges.
Determining impairment has emerged as a key issue in the debate.
Current NSW laws, introduced in 2007, mean a motorist can be charged if any trace of the psychoactive component of cannabis (THC) is detected in their system.
This can happen after a blood test or a roadside saliva test.
The federal government legalised the use of medicinal cannabis in 2016, but the NSW law remains the same.
Doctor Joel Wren, from the Society of Cannabis Clinicians, today told the inquiry the current laws were "archaic" and "nothing short of discrimination".
He said the driving laws surrounding medicinal cannabis should be consistent with other prescription therapies such as opioids.
"We are widely prescribing these medications every single day to many Australians and we are telling them it is okay to wait a while if you feel impaired, that some people do metabolise these medications differently," Dr Wren said.
Impairment a key issue
But the Standing Committee on Law and Justice was told determining a cannabis user's level of impairment could be tricky.
Doctor Danielle McCartney, from the University of Sydney's Lambert Initiative for Cannabinoid Therapies, told the inquiry she had done extensive work in the field using driving simulators and computerised cognitive-function tests.
"Obviously not all of that is practical at the roadside," she said.
"There are of course the field sobriety tests, which are used internationally in order to identify people who are not safe to drive."
The Lambert Initiative's Professor Iain McGregor said the traditional test of getting a motorist to walk in a straight line did not work well for cannabis users.
"Cannabis people seem to be able to walk the straight line quite well," he said.
Doctor Thomas Arkell, from Swinburne University, told the inquiry he had some reservations about the test.
"Some people find that very hard anyway," he said.
"Particularly in older people, when your balance tends to get worse, especially if you have hip or keen problems."
The inquiry has heard 180,000 applications for medicinal cannabis use had been approved by the Therapeutic Goods Administration as of October 12, 2021.
The number of active patients in Australia in September last year was estimated at 70,000.
Crash risk debate
A submission to the inquiry from the NSW Government suggested the presence of THC in a driver's system increased their crash risk by 50 per cent.
Professor Lambert disputed that figure, but conceded the data was complex.
"What they call the odds ratio is about 1.1 to 1.4 if you are acutely intoxicated with cannabis," he said.
"In other words it's an increased crash risk of 10 to 40 per cent.
"That is about the same as 0.04 or 0.05 blood-alcohol concentration, and is significantly less than you would see with opioids or benzodiazapines or sedating anti-depressant drugs that are very widely prescribed.
Fatal crash factor?
But the inquiry was told the NSW Government had no intention of changing the law.
The state's head of Transport Safety, Peter Dunphy, said between 2016 and 2020 there were 253 fatal crashes involving drivers and riders with THC in their system.
"This represents about 16 per cent of all fatal crashes and approximates to one fatal crash every week," he said.
"THC can affect the cognitive and motor skills necessary for safe driving.
"While it is true that much of the evidence for impairment impacts are from illicit THC use, there is still evidence that medicinal THC users can be impaired for a period of time.
Mr Dunphy said cannabis was different from other drugs, because there was no way to distinguish between medicinal and recreational use.
"Until there is clear evidence on the effects of medicinal cannabis on driving, the NSW Government will continue to take a cautious approach," he said.
Greens MLC Cate Faehrmann challenged the validity of statistics quoted in the government's submission, suggesting the fact THC was present in a driver's system did not necessarily make it a factor in a fatal crash.
The committee will present a report to parliament in early August.
