Study To Determine Impact of Cannabis on Driving Ability Delayed

A trial will determine how cannabis impacts driving ability and provide guidance for medical cannabis policy in Victoria, Australia.

An Australian trial that will investigate the impact of medical cannabis on driving ability won’t be finished until late 2025. The Guardian reports that Australian cannabis advocates are disappointed that the Victorian government appears to be delaying the study despite the issue being called a priority.

In February 2023, then-state premier Daniel Andrews pushed to determine how cannabis impacts driving ability and said that the issue is a priority for the Victornian government. He estimated as many as 200,000 medicinal cannabis patients in Victoria are essentially restricted from driving. 

That’s because THC can be detected in the body for weeks, if not months after consumption, meaning medicinal cannabis patients can essentially never drive without worry of driving while what authorities consider to be impaired.

Victorian premier Jacinta Allan announced May 14 that Swinburne University of Technology in Melbourne, Australia has been selected to run the trial. The $4.9 million dollar trial ($3.26 million USD), to be completed over 18 months , will review about 70 medicinal cannabis patients’ ability to manage distractions and assess their performance behind the wheel, including steering, braking, and speed control on a dedicated track.

“Just as we were the first state in the nation to introduce medicinal cannabis to support people with their medical illnesses, we are now moving to have this world-first trial to support and examine how it affects people as they’re out on this closed circuit driving track,” Allan said.

Victoria became the first Australian state to legalize medical cannabis in 2016, but it remains illegal for individuals to drive with any trace of THC in their bloodstream.

Legalise Cannabis MPs David Ettershank and Rachel Payne said they were disappointed in the timeline. “Jacinta Allan may be on a driving track today but I know she is intentionally ‘stalling’ on this decision,” Payne said. “In 2023, Dan Andrews promised an answer ‘in coming months’ followed by a guarantee to have it fixed by 2024. Now, with a new premier, it’s mid-2026 at best.” Ettershank suggested was “discriminating” against medicinal cannabis patients and the motives were political.

What could change? Already in Tasmania, leaders established a medical defense if drivers are caught behind the wheel with THC in their system, as it can linger there for weeks or months. But roads minister, Melissa Horne said Tasmania had far fewer medicinal cannabis patients than Victoria. “At the heart of it, it is a basic human rights issue where we’ve got people out there who are taking a legally prescribed substance who cannot drive at the moment,” she said.

While cannabis breathalyzers have emerged, made by several companies, there is currently very few, if any places in the world that has developed standardized cannabis impairment testing; All that exists are tests that can detect THC in the bloodstream, but that has little to do with current impairment. That could change quickly, however.

How Long Cannabis Impacts Driving Performance

Researchers in Australia have been determining the window that cannabis can impair driving performance. In one case, Thomas R Arkell, Danielle McCartney , Iain S McGregor, who are associated with The Lambert Initiative at the University of Sydney, studied the impact of cannabis on driving ability.

They determined that cannabis can impair driving ability in the hours immediately after smoking, but the impairment ends well before THC metabolites are flushed from the bloodstream.

“Patients using THC-containing products should avoid driving and other safety-sensitive tasks (e.g. operating machinery), particularly during initiation of treatment and in the hours immediately following each dose,” the authors wrote. “Patients may test positive for THC even if they do not feel impaired, and medical cannabis use does not currently exempt patients from mobile (roadside) drug testing and associated legal sanctions.”

Hound Labs, based in Oakland, California, said in 2021 that market release is imminent for its Hound Marijuana Breathalyzer, which can detect the presence of THC molecules in the breath.

“The first commercial units of the Hound Marijuana Breathalyzer will be in the hands of customers this spring,” Dr. Mike Lynn, an emergency room physician who is CEO and co-founder of Hound Labs, told High Times. “Production will ramp up throughout the rest of 2021.”

The introduction of the Hound Breathalyzer could really shake things up for law enforcement, motorists, employees, employers, and medical cannabis patients. It’s different from other drug tests because Hound Labs reps say it can test whether the person is currently high, as measured by the presence of THC molecules in the breath. The developers of the Hound believe that THC molecules linger in the breath for up to four hours after smoking. 

In the U.S., 12 states—Arizona, Delaware, Georgia, Indiana, Iowa, Michigan, Oklahoma, Pennsylvania, Rhode Island, South Dakota, Utah and Wisconsin—have zero-tolerance laws for certain drugs including THC.

  1. Interestingly both Hound Labs research and the Sydney University research quoted found that there’s a window of roughly 4 hours of impairment following cannabis consumption (via inhaling smoked or vaped THC), which means a ‘positive’ reading from both the Hound Labs breathalyzer as well as the saliva testing (immunoglubulin) available can suggest that a person has recently consumed cannabis/THC.
    BUT Hound Labs suggestion that its breathalyzer “can test whether the person is currently high, as measured by the presence of THC molecules in the breath.” and the similar suggestion that a positive saliva test suggests impairment are DISTORTIONS OF THE TRUTH.
    In fact neither technology measures the amount of THC molecules in a persons breath or saliva (quantitative analysis) and even if they did – there is no direct correlation with THC breath or saliva levels and serum/blood levels as there is with Alcohol. Also research (including that done by Sydney University) has shown there is consistent correlation with serum/blood THC concentrations and the level of impairment/intoxication.

    The FACT is that consuming a single low dose THC edible (eg a CBD edible) or taking a single drag of a joint of low THC cannabis with a non-intoxicating (insufficient) THC dose will result in a true positive test result from both a saliva test and the Hound Lab Breathalyzer resulting in that person being wrongly (without real evidence) being accused of being impaired.


    “Also research (including that done by Sydney University) has shown there is NO consistent correlation with serum/blood THC concentrations and the level of impairment/intoxication.”

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