4 Questions That Uncover the Problem With Our Current Drug Driving Laws (& Medicinal Cannabis)

Read time: 2.8 min read

This article is written by Drive Change ambassador Michael White. Below, he shares his experienced insight and analysis of recent data on medicinal cannabis and its effects on driving.


As a person who has been involved in drug-driving policy and research for over 25 years, I have recently been asked to provide answers to the following four questions in relation to the road-safety implications of driving after using cannabis. 

These are probing questions that get to the heart of the matter. They are the questions that policy makers need answers to, if they are to develop evidence-based policies in relation to driving after the use of cannabis.

Q1. Does research show that risk of crashing when there is THC in the bloodstream are significantly higher than when there is no THC in the bloodstream (based on an unbiased odds-ratio calculation)? 

My answer is ‘no’ – when study biases are taken into account. 

In other words, the presence of THC in the blood is not associated with a higher risk (odds ratio) of crashing. To come to this conclusion I reference a recently completed epidemiological review1 of the cannabis-crash literature that I have co-authored with my colleague Prof Nick Burns (White & Burns, 2021), which is that the null-hypothesis (cannabis-crash odds ratio = 1.0) cannot be rejected. 

However, that statement of our conclusion is, of course, compatible with the true odds ratio being slightly greater than 1.0 – such as 1.2. However, my opinion is that the true odds ratio most probably really is 1.0. 

Q2. Does research show that driving performance is degraded when there is THC in the bloodstream compared to when there is no THC in the bloodstream?

Yes, so we have a problem. 

Why does the degradation of performance (impairment) not increase the cannabis-crash odds ratio? There are many things to be taken into account. Cannabis users are not inclined to drive soon after using, especially if they feel intoxicated. Cannabis impairment is generally weak, and probably normally below a threshold where driving performance is dangerously degraded. 

Furthermore, while there could be a small increase in crash risk due to impairment, it is probably balanced by a small decrease in crash risk due to more cautious driving (as demonstrated by slower travelling speeds and greater headways).2

Given the role of speed in crash causation, a little extra caution could go a long way. Nick Burns and I are working together again to review the literature of the impairing effects of cannabis.

Q3. If medicinal cannabis has effects on driving performance, then is there a time window after ingestion of THC when impairment is most likely to degrade driving performance? 

Yes, there is a time window. Its duration has been explored in a couple of recent reviews.3 4 The most conclusive evidence we have so far is this:

For smoked cannabis, it is probably about three hours from the moment it is ingested. For edibles, such as cookies, it is probably a bit longer, starting after a delay of at least half-an-hour. The two aforementioned reviews also indicate that low-level impairment can, in some cases, last beyond three or four hours.

Q4. Does a performance-based test exist which can measure any decrease in performance that might arise from having THC in the bloodstream?

No. There is too much individual variation in any performance tests and too much individual variation to be able to accurately gauge levels of THC impairment. However, the answer could possibly be ‘yes’ if baseline levels of performance could be established for individuals. 

Still, even then, the measured performance decrement due to THC would probably be irrelevant to crash risk.  

There is a smartphone app known as the ‘DRUID test’ that seems to be popular in some quarters for measuring driver impairment. A recently published paper that includes an evaluation of the test can be viewed from the journal’s website here.


  1. For a copy of this review, please email a request to mawhite8@internode.on.net.
  2. White, M. A., & Burns, N. R. (2021). The risk of being culpable for or involved in a road crash after using cannabis: A systematic review and meta-analyses. Submitted for publication.
  3. Eadie, L., Lo, L. A., Christiansen, A., Brubacher, J. R., Barr, A. M., Panenka, W. J., & MacCallum, C. A. (2021). Duration of neurocognitive impairment with medical cannabis use: A scoping review. Frontiers in Psychiatry, 12, Article 638962.
  4. McCartney, D., Arkell, T. R., Irwin, C., & McGregor, I. S. (2021). Determining the magnitude and duration of acute delta-9-tetrahydrocannabinol-induced driving and cognitive impairment: A systematic and meta-analytic review. Neuroscience and Biobehavioral Reviews, in press.

For Blake, Queensland Drug Driving Laws are Unreasonable

Read time: 1 minute

Blake is sharing his experience as part of our “Personal Stories” series, which invites medicinal cannabis patients to share with the community how drug driving laws are impacting their quality of life. If you’d like to share your story, please email us at hello@drivechangemc.com.au


It’s time that medicinal cannabis patients in Queensland are given driving defence. 

I’m a medicinal cannabis patient, and every day I worry that if I were to get drug tested that it would screen positive. 

It’s not fair that I should have to worry about this, since using my medicine doesn’t mean I drive when I’m impaired. Having access to medicinal cannabis has been a godsend for my condition, but knowing about the consequences if I test positive in a drug test only brings anxiety.

I use medicinal cannabis to treat my bipolar disorder. I’ve grappled with this for a long time, and access to medicinal cannabis has helped to save my life. 

However, the laws make it seem like the system still doesn’t accept medicinal cannabis. It’s unreasonable to suggest to people who use medicinal cannabis that they can “just go without for a few days” to be able to drive. The laws should take into account having THC in your system doesn’t mean you’re impaired.

I have the proper paperwork from the TGA, stating that THC may take up to five days for most of the THC to leave your system. To be able to work, I can’t wait that long before driving again. These laws are keeping me out of work and struggling to earn an income. If I choose to drive anyway, I am at risk of losing my license, even if I’m not impaired. It’s just not fair.

Cannabis Improved His Life After the Army, but Driving Laws Stand in the Way of His Freedom

Read time: 2 minutes

Cody is sharing his experience as part of our “Personal Stories” series, inviting medicinal cannabis patients to share with the community how drug driving laws are impacting their quality of life. If you’d like to share your story, please email us at hello@drivechangemc.com.au


Hi, my name is Cody. I’m 30 years old living with my partner and two beautiful kids in the northern suburbs of Adelaide. I have been a medical cannabis patient since April 2021, but my journey began around 7 years ago.

In 2013 whilst serving in the Royal Australian Army, I suffered an acute knee injury that transformed into chronic pain. I have had multiple surgeries and countless hours of physiotherapy, none of which solved the problem. While I was dealing with this chronic pain, mental health issues began to develop. As a result, I was medically discharged in 2015. I had served 6 1/2 years.

Cody relies on a driver’s licence to keep his job and provide for his family. The drug driving laws pose a threat to his livelihood and his wellbeing.

Somewhere along the way, I had also developed a terrible relationship with alcohol, abusing it to numb both my body and mind. This lasted five years. I’m sober now, having not touched a drop since December 2020, but I attribute much of that success to my amazing family and psychiatrist.

In the past, I sought conventional drugs to cope with my struggles. Antidepressants and strong opioid-based medications have been regular medications for me since 2014. As time progressed, I began taking benzodiazepines and sleep aid medication.

In my experience taking these drugs over the years, I’ve had a handful of unintentional overdose experiences. It’s very concerning how easily this can happen. This ranged from skin itches and rashes to becoming violently ill and losing consciousness.

It would be safe to say that I’ve had my fair share of traditional prescription medication.

In an attempt to relieve me of my dependence on these troublesome drugs, I obtained a legal prescription for cannabis. It quickly became clear that there were benefits of cannabis on both my physical and mental state. I had no adverse effects from cannabis, leaving me stumped as to why medicinal cannabis wasn’t more widely accepted.

Starting to medicate with cannabis has been the best medical choice I have ever made. At least 90% of my medication is cannabis. As a result, my dependence on both opioids and benzodiazepines has plummeted.

However, the biggest problem I have with medical cannabis is the unfair and discriminatory drug driving laws across the country, specifically in my current state of South Australia.

Like a lot of people, I work and need a licence to do so. However, every time I get behind the wheel I run the risk of testing positive for THC at a roadside drug test, even several hours after the impairing effects have worn off.

It makes you feel like a bit of a criminal. Unfortunately, this is a common feeling amongst the medical cannabis patient community.

Medicinal cannabis patients shouldn’t have to choose between medicating or keeping a driver’s license and job. If someone is prescribed medicinal cannabis and they’re not driving impaired then they should not be guilty of an offence.

These laws need to change immediately, the current legislation is discriminatory, outdated, and maintained purely through ignorance.

I have seen and also personally experienced such a positive outcome that medical cannabis has to offer, I beg everyone involved in the legislation of this: please reform these unfair laws now.


You can help be an agent of change for these unjust laws by signing our petition.

One Size Does Not Fit All: Mick Palmer on the Need for Fit-For-Purpose Driving Laws in Australia

Read time: 3 minutes

This article is written by Drive Change ambassador and former Commission of the Australian Federal Police, Mick Palmer. Below, he shares his take on where the laws need improvement to protect medicinal cannabis patients and the community on the road.


There is a clear and well-understood correlation between impaired driving and road safety. Australia’s road toll is of broad community concern, and the Government’s effective policies–like the .05 drink driving legislation and speed cameras– should be applauded. However, Australia’s ‘zero-tolerance’ drug driving policy creates trouble for both patients and police. 

“Fit-for-Purpose”

The government has already allowed for doctor-approved access to medicinal cannabis. This comes in response to the ever-growing scientific evidence, in addition to anecdotal evidence, that medicinal cannabis provides relief for people experiencing genuine pain and suffering due to a range of health issues, including terminal illness.

The government’s recognition of this evidence provides a step toward relief for thousands of Australians. However, for the legality of medicinal cannabis to fully operate as intended, the roadside drug testing protocol urgently requires amendment. 

I am not suggesting impaired driving laws should be weakened, but rather that they are updated to fit-for-purpose and aimed at achieving intended outcomes. 

To become fit-for-purpose, retain credibility, and operate fairly, driving laws must be aimed at dealing with impaired driving. Until this happens, many law-abiding Australians suffering from illness and often extreme pain will continue to experience legal and physical distress as a direct result of the discriminatory drug driving laws. 

“Police Leniency”

Likewise, police have a clear responsibility to effectively manage and apply the legislation in the community interest. The truth is that police exercise considerable compassionate discretion in their enforcement of drug driving laws every day. This is, in part, due to the driving laws being unfit-for-purpose and in need of review and amendment, or repeal.

The role of the police is to enforce laws, not make them. It is certainly a recipe for inconsistency to expect the police to cure legislative deficiencies by making personal judgments on patients. 

Furthermore, if police are screening for medicinal cannabis use but not for impairment, the laws are unfit-for-purpose and end up punishing people already coping with a terminal illness or serious pain.

Medicinal cannabis patients should not need to rely on the favourable exercise of discretion by police to escape punishment. It is up to Governments to have the courage and decency to legislate the necessary changes.

“Necessary Changes”

If there is any chance that medicinal cannabis can help people with terminal illness or serious pain, to lessen their pain and suffering and improve their quality of life, we should, as an educated and compassionate society, do all that is reasonably possible to facilitate access. 

The fact that these current drug driving laws exist is sufficient for many patients who qualify for medicinal cannabis treatment to decide not to take their medication. 

Some of these patients need to drive their motor vehicles as a matter of daily necessity. Sufferers should not be forced into situations where they may end up breaking the law to gain relief. Surely this is not the government’s intention.

The reality of current roadside testing is that they are not only discriminatory, but also invariably lead to further distress, fear, and embarrassment for the patients.

The resulting pain and suffering achieve the exact opposite of the intention of Governments in allowing legal access to medicinal cannabis in the first place. I am personally confident that this also is not the intention.

The facts speak for themselves. There is a better way to uphold law and road safety. We must be prepared to explore the options. 

As an example, Norway has successfully been assessing drug levels in driver’s systems for many years. This surely is far preferable to the continuation of a “zero-tolerance” approach that we have here, which can only be beaten by judicial discretion.

The current medicinal cannabis drug testing laws need to be subject to urgent review. By amending the laws, we move to ensure they operate fairly and without discrimination while continuing to achieve the intended outcome of controlling impaired and potentially dangerous driving.