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In 2016, Australia legalised access to medicinal cannabis, allowing patients to access dozens of different cannabis products through prescriptions.
Now the Victorian government wants to take another step in opening the door for medicinal cannabis patients in the state to be able to drive.
In a bill passed last year, the government committed to launch a closed-circuit trial to research the impairment that medicinal cannabis causes on driving.
A push to change driving laws around medicinal cannabis has also been seen in other states such as Western Australia, while in Tasmania it is legal to drive as long as a person is not impaired by the drug.
But how does medical cannabis legislation work, and what are the risks to road safety?
Medical cannabis in Victoria explained
Any Victorian patient, with any medical condition, can be prescribed medicinal cannabis by their doctor if they believe it is clinically appropriate.
There are two groups of medicinal cannabis patients, with different driving rules applying to each of them.
Medicinal cannabis patients using cannabidiol or CBD products have always been allowed to drive in Victoria as long as they are not impaired.
However, some medicinal cannabis products contain a compound known as Delta-9-tetrahydrocannabinol or THC, which is responsible for the "high" feeling associated with cannabis and could impair driving ability.
It is currently an offence in Victoria for a person to drive with any amount of THC in their system, whether the THC comes from medicinal cannabis or not.
Victoria Police currently conducts random roadside drug testing throughout Victoria, with saliva tests that are positive for THC resulting in a drug-driving charge.
Drivers with THC in their system faced mandatory licence suspensions and fines if caught.
The new trial by the government will seek to test just how impaired people with medicinal cannabis in their system are whilst driving.
How will the trial work?
Drivers who use medicinal cannabis will be taken around driving courses with an instructor at special closed road facilities such as METEC in Bayswater North and AARC in Wensleydale.
Minister for Roads and Road Safety Melissa Horne said the trial, conducted in partnership with Swinburne University, would be a world-first.
"There is nowhere in the world that actually has got that standard way of measuring impairment through medicinal cannabis," Ms Horne said.
"It is a basic human right — we've got a legally prescribed drug, let us be able to measure what that looks like in a road safety environment."
About 70 participants will take place in the trial, due to begin in September this year.
When first announced last year, the trial was praised by legal groups such as the Australian Lawyers Alliance, who have dubbed driving laws penalising medicinal cannabis users as "outdated and unfair".
"Cases are coming before the courts every week where people are losing their licence and their livelihood because they are taking prescribed medicinal cannabis and driving," Australian Lawyers Alliance spokesperson Greg Barns said.
"Drivers who take opioids or other prescription medication do not find themselves in court or risk losing their license, and neither should drivers who have taken a prescribed and legal dose of cannabis."
Ms Horne would not however say when any potential law changes would be passed if the trial is found to be successful, with results due in 2026.
Is it dangerous to drive with THC in your system?
According to the VicRoads website, THC is a psychoactive substance that has been shown to impair cognitive and motor function, increasing your risk of being involved in a motor vehicle crash.
A meta-analysis of studies conducted in 2021 found cannabis increased the risk of crashes somewhere between 11 and 42 per cent.
Researchers found the added crash risk from cannabis similar to that of the legal blood alcohol content (BAC) limit for driving, with the high end of estimates similar to that of prescription drugs like antidepressants.
Internationally, there is a lack of research on the effects of cannabis on driving impairment.
In the United States, where recreational cannabis is legal in some states, the drug is the second most frequently found substance in the bodies of drivers involved in fatal motor vehicle accidents after alcohol.
A study of emergency department presentations in Canada, which legalised cannabis in 2018, showed no evidence of significant changes in traffic-injury emergency departments.
Driving while drug-impaired remains illegal in both countries, but the measurement of what constitutes impairment differs across state and country lines.
In Canada, any reading above 2 nanograms (ng) of THC per millilitre of blood while driving is considered an offence, while in the US state of Colorado that figure is 5ng or above.
Meanwhile, in states like New York and California, penalties are based on whether law enforcement can prove a driver has been impaired by a drug.
For now, the Victorian government has not made clear what any introduced driving laws may look like, should the trial be successful.
How have medicinal cannabis advocates reacted?
Legalise Cannabis MPs have criticised the government for moving too slowly on the issue, saying millions of dollars are being spent to conduct research that has "already been done".
"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. She's in the slow lane," MP Rachel Payne said.
“Given the 10-year time blowout, I am calling on the premier to follow Tasmania’s lead and allow Victorians, unimpaired and prescribed medical cannabis, to drive without fear of recrimination."
Ms Payne noted a similar study that had already been conducted by Swinburne University, where 40 people were tested on a virtual driving simulator after consuming medical cannabis, as opposed to a real vehicle and road as planned in the new trial.
The Australian Legal Alliance has also called for the prosecution of medicinal cannabis patients who are driving while unimpaired to be paused while the trial is undertaken.