South Australia’s zero-tolerance approach to drivers with cannabis in their system has been blasted by legal experts during a parliamentary inquiry calling unanimously for change.

Drivers who test positive to tetrahydrocannabinol (THC) during roadside drug testing of their oral fluids and blood in SA can lose their licence immediately for three months.

But THC can stay in a person’s system for many days, “long after the high is gone”, according to SA Police’s own marketing, with ramifications for those legally prescribed medicinal cannabis.

Southern Cross University Dean of Law and Chair of Discipline David Heilpern is a former NSW magistrate who regularly dealt with people in court who tested positive after taking prescribed “cannabis drops or leaf” in previous days.

“As a magistrate, I just couldn’t stomach it,” he told SA’s Joint Committee on the Legalisation of Medicinal Cannabis earlier this year.

“People’s lives are destroyed by loss of licence, particularly in rural and regional areas.

“Single mums lose their ability to take their kids to sporting events and educational opportunities … these are real costs, and for what benefit?”

SA has one of the country’s largest medicinal cannabis farms. (ABC News: Tony Hill)

Mr Heilpern wants laws amended to allow a defence for medicinal cannabis users — provided they are using it in accordance with their prescription and are not impaired at the time or driving under the influence.

Tasmania is currently the only state with such provisions.

Cross party committee unanimous

The joint committee, which included two Labor and Liberal elected members, an independent, and Greens MLC Tammy Franks as its chairperson, last week unanimously made 13 recommendations in its interim report.

This included amending SA’s Road Traffic Act so it would not be an offence to drive with THC present in oral fluid or blood when a driver:

  •     has been prescribed medicinal cannabis containing THC
  •     is using the product in accordance with the prescription
  •     has a zero-blood alcohol concentration, and
  •     the driver is not impaired.

A SA government spokesperson said it would consider the recommendations in “due course”.

“The government is open-minded to further improvements while ensuring road safety outcomes are maintained and any action taken is informed by research,” the spokesperson said.

‘Not based on science’

Australian Lawyers Alliance senior counsel Greg Barns said the ban on having any THC in a person’s system was “not based on science”.

A test used by Australian police to detect the presence of illicit drugs. (Supplied: ACT Policing)

He said there was a two-year trial underway in Victoria looking at how much medicinal cannabis “you can have in your system before you are a risk to other road users”.

Mr Barns told the inquiry research was also underway in the United States and Canada to set an “impairment level such as we have in relation to drink driving to end this sort of injustice”.

The ABC has requested data from SAPOL about how many people have lost their licence since the new laws came into effect during February 2023.

SAPOL State Operations Service Assistant Commissioner Ian Parrott told the inquiry that preliminary data found of 483 road users involved in a crash causing loss of life or serious injury in 2023, 81 of them had THC present in their system.

In response to questioning, he also said that of 5,057 drivers involved in fatal or serious injury crashes in 2018-2022, just 5 per cent, or 229, had THC in their system on its own without any other drugs present.

Ian Parrott says there are large variances in the strength of medicinal cannabis. (ABC News: Lincoln Rothall)

Mr Heilpern challenged statistics hinting at a “causal relationship” between the presence of THC and crashes.

He said when national statistics had found about 12 per cent — up to 18 per cent in some areas — of males aged 18 to 25 used cannabis, the presence of cannabis could be expected and it did not mean it was “responsible for any single one of those deaths”.

Assistant Commissioner Parrott told the inquiry there was a difference between an offence for a substance’s presence, and the offence for driving under the influence (DUI), which was determined by a police officer’s observations and followed by testing.

“Regardless of whether that impairment test is met, for the purposes of reaching a threshold for driving under the influence as per the legislation, I don’t know of anywhere that has settled on a presence limit for THC … in a person’s system that has been defined as being a safer amount,” he said.

‘Dodgy assumptions’

Ms Franks said the punitive nature of SA’s drug driving laws and roadside testing was criminalising those using medicinal cannabis without any evidence of impairment.

“And that is fine if you’re a police officer and you like black and white law,” Ms Franks said.

Committee chairperson Tammy Franks says current laws are based on “dodgy assumptions”. (ABC News: Che Chorley)

“If cannabis is illegal, then presence is illegal — but once we changed the laws back in 2018 federally to allow for lawful medicinal cannabis to be prescribed to patients who are sick … surely our criminal law should change as well?

“Safety and science should lead this debate; not dodgy assumptions.”

Seeking better technology

The committee also recommended the government monitor emerging roadside testing technologies to identify more accurate methods to measure THC levels for impairment.

In New Zealand, for example, the Ministry of Transport said roadside oral fluid testing was on hold because a “suitable device that met the device approval criteria in the legislation wasn’t able to be identified”.

The country’s drug driving laws, which include a medical defence for drivers using medicinal cannabis with a prescription, also include different levels of offences and penalties for drivers on varying levels of impairing drugs.

Adelaide traffic lawyer Karen Stanley said she had seen a surge in clients losing their licences for false positives from roadside testing since SA’s laws had come into effect.

“The ability of police to issue an immediate disqualification has meant there has been a large amount of people who lost their licences for a few weeks until the forensic science tests came back negative,” she said.

A study by the University of Sydney’s Lambert Institute tested two of the mostly commonly used mobile drug testing devices and found neither demonstrated the recommended greater than 80 per cent sensitivity, specificity and accuracy rate.

But Ms Stanley did not believe people with a medicinal cannabis prescription should be allowed to drive “with impunity”.

She said there needed to be a roadside test based on impairment rather than presence.

“There are a lot of lawyers around Australia who are calling for that, but the government doesn’t seem to care,” Ms Stanley said.