When cannabis products were legalized in Canada, a panic ensued among road safety and public safety groups alike: legalization would lead to an increase of cannabis-related impaired driving incidents.
And while statistically that has now been shown to be an unjustified hullabaloo about nothing, there is a definite trend of impaired driving involving cannabis that warrants more consideration.
You see, impaired driving caused by cannabis is almost never a solo-factor. Rather, cannabis is almost always seen in conjunction with other drugs or with alcohol.
It is not clear whether this connection is due to the potential increase in the impairing effects of cannabis when combined with other drugs or whether it is because of the fact that cannabis is difficult to detect, but the science seems to support one thing: combined cannabis and something else driving is the real concern.
Take, for example research done in Australia by Boorman and Papafotiou in 2007. Australia was one of the first jurisdictions to enact drug-impaired driving testing programs, including the use of salvia testing. The results of the testing showed that most people who tested positive for cannabis were also detected as having medically-prescribed drugs. And the cause of their impairment appeared to be the effects of medical or prescription drugs, rather than the cannabis.
Does this mean that people who take prescription drugs that can impair driving should not drive? Of course not. But it does mean we may need to take a better look at how public safety and road safety programs are employed when it comes to medical users of all drugs, not just cannabis.
In Canada, for example, we do not test for most medically-prescribed drugs using our saliva testing. And the Drug Recognition Evaluation program also does not distinguish between identifying a medically-prescribed drug in a person’s body and a medical drug that is not prescribed or is not taken in accordance with the prescription.
In the Australian research, Boorman and Papafotiou noted that cannabis was almost always found in conjunction with other drugs, rather than just on its own.
This trend is not exclusive to cannabis either. Only 18% of drivers who tested positive for drugs and were determined to be impaired showed a single drug in their system. This means that 81 out of 100 drug-impaired drivers were taking more than one drug. Was it a combination of drugs that caused impairment? Poor monitoring for drug interaction on the part of doctors that led to findings of impairment by a drug? It’s hard to say, but these are very real risks.
In fact, cannabis rarely showed up. It was only present in a little over 13% of drivers, and for the single-drug category, it is likely that only 2.4% of drivers were determined by police to be impaired by cannabis alone. And once you adjust for police and testing errors, this is really an insignificant amount of people on the road actually impaired by cannabis on its own.
Now, you may say these studies are specific to Australia, a country that does not have legal cannabis, and thus are not helpful in assessing British Columbia or Canada’s drug-impaired driving problem in a post-legalization world. However, the research results are repeated in other jurisdictions.
A study in Norway, for example, looked at 112,348 Norwegian drivers who had been arrested for suspected DUI. This included alcohol and drugs. The study covered a broad time range, from 1990 to 2015.
Importantly — 11% of those arrested had NO DRUGS and NO ALCOHOL whatsoever. They were totally sober. That’s a pretty high false arrest rate for alleged impaired driving, and supports that these tests used by police can be improperly conducted and interpreted.
But, just like in the Australian research, the vast majority of drivers showed a combination of drugs and alcohol, or a combination of drugs and not one single drug as the cause of their impairment. This is, of course, after removing 11% of the participants — over 11,000 people — who were falsely and wrongfully arrested and accused.
The overall rate of impairment by cannabis? Only 21.5%. That’s not even double the number of factually innocent people.
And 2023 research out of Norway looked at 10,520 drivers from 2013 to 2020. Changing attitudes and reduction of stigmas about cannabis did not appear to explain the numbers: only 20.3% (a reduction from the earlier Norwegian study data) showed impairment by THC.
And of those 2100ish drivers who tested positive for cannabis impairment, only 15.7% of them were using THC on its own. So only 3.2% of drivers were found to have actually had impairment by cannabis on its own, in a sample size of over 10,500 people. Again, an almost insignificant number for the hue and cry that existed over legalization in BC.
Meanwhile, a 2024 study done in Colorado – a state with more legal drugs than we have in Canada – still showed no major numbers of drivers impaired by cannabis alone. In that study, done by Wood, the author found that only 11% of DUI offenders in Colorado state had cannabis as the sole cause of impairment.
Cannabis DUI driving is simply not a real concern for the public safety. It is not something that is occurring on its own with much prevalence and the studies that have been done in this area very clearly show that it is other drugs that are more likely to be the culprits in impaired driving cases.
