Impairment Vs Presence Of Cannabis: The International Cannabis Driving Debate Continues

Around the world, the debate continues about how to quantify the presence of cannabis in an individual’s system and how it relates to their ability to operate a vehicle. 

Nobody in this debate believes that anyone unable to drive should get behind the wheel of a car. Instead, the issue lies in the difficulty of creating a one-size-fits-all rule for a very complicated issue: how to judge if someone is too impaired to operate a vehicle. 

Various parties have proposed multiple metrics, including the presence of cannabis in saliva, the levels of cannabis in the blood, and actual impairment.

Cannabis And Driving Laws In The USA

For more than two decades, the U.S. has studied the effects of cannabis on driving and has a wealth of information to draw upon. However, despite the volume of studies, policymakers have not reached a consensus, which is not surprising given the biological nuances of cannabis (versus a substance like alcohol). 

One of the main issues behind defining impairment is the quantification of cannabis in the system. When one smokes cannabis, the absorption and impairment vary widely depending on several factors. 

Suggested Strategies To Address Cannabis Consumption And Driving In The U.S.

A suggestion to address the issue of cannabis consumption and driving is a three-level approach to quantifying impairment. 

The first level is effect-based. Here, law enforcement officers look for proof that there is impairment and it is due to the consumption of a drug. Commonly accepted tests like the ability to walk in a straight line may demonstrate that a driver is impaired. An effect-based approach can help to offset the fact that different cannabis consumption methods produce the strongest effects at disparate times; smoking cannabis has its most potent effects for the first 20 to 30 minutes after smoking, while oral dosages may take effect after one hour of consumption. 

If the effect-based method is unclear, law enforcement may measure the amount of THC in an individual’s system. However, unlike alcohol, THC can remain in the system for long periods and build up over hours, days and months, making it very difficult to establish a simple presence rule. 

The third level of testing is a quantitative threshold. Many U.S. states have adopted a valuation system based on the presence of THC in the bloodstream, though that level varies considerably from state to state. In Ohio and Nevada, more than 0.2 ng/ml of blood is considered impaired, while in Colorado, Illinois, Montana, and Washington, 0.5 ng/ml is considered impaired. Additionally, a 2007 study suggested that 0.7 to 1.0 ng/ml qualifies as impairment. A follow-up government piece from 2019 essentially reaffirmed this stance. Despite existing laws, a recent study cast doubts on the ability to actually set quantifiable limits to measure impairment from THC. Simple presence is not the answer, and setting safe and fair impairment standards is proving difficult. 

German Laws Governing Cannabis And Driving 

Germany, UK and Australia are the two most progressive global medical cannabis countries grappling with the issue of cannabis impairment and driving right now. German contributor Atilla Ldil expands on the country’s approach:

“Currently, German cannabis driving laws differentiate between medical patients and ‘recreational’ consumers, but these laws continue to cause significant problems for patients. Despite being legally permitted to drive when following medical guidelines, enforcement remains inconsistent. Arbitrary police stops, expensive and burdensome tests, as well as sanctions from licensing authorities not only threaten the financial security of many patients but often their professional future as well. Psychological evaluations, which many are required to undergo, are costly and frequently conducted by evaluators who are critical of cannabis, leading to negative assessments — even when patients pass the tests. As a result, some patients lose their driving license and, with it, the ability to pursue their profession or manage their daily lives independently. The life stories of these individuals are marked by discrimination, stigmatization, and existential threats, all of which are exacerbated by a legal system that still does not fully accept the use of cannabis, even for medical purposes. 

The new THC threshold of 3.5 nanograms applies only to recreational users, not patients. Drivers without impairment and with a blood THC level below this limit should not face additional penalties or evaluations. However, many patients continue to face severe discrimination and costly bureaucratic hurdles regarding their driving rights.”

Cannabis And Driving Laws In England

English contributor Rupa Shah of Relief U.K. provides an inside perspective on cannabis and driving laws in the U.K.:

“In England, cannabis driving laws center around the presence of THC in a driver’s system, with strict enforcement despite the evolving landscape of medical cannabis. The current law sets a very low legal limit of 2 micrograms of THC per liter of blood, reflecting a zero-tolerance stance. Police assess impairment through a combination of observational tests, such as checking for bloodshot eyes or unusual behavior, and formal roadside impairment tests, like walking in a straight line. Additionally, oral swabs are used to detect the presence of THC, though these tests only indicate recent use, not actual impairment​.

If a driver is suspected of impairment, they may be taken to a police station for a blood test, which becomes the primary evidence in drugged-driving cases. While the presence of THC over the legal limit results in penalties, this approach has been criticized for failing to distinguish between impairment and residual traces in medical cannabis patients. The medical defense allows for driving with a prescription, provided the driver is not impaired, yet patients still face legal challenges due to the discrepancy between presence and impairment​.

The lack of correlation between THC levels and impairment raises concerns about fairness, particularly for medical cannabis users who may have elevated THC levels without any functional impairment. Calls for reform suggest adopting a more nuanced approach, akin to Germany's differentiation between medical and recreational users, to balance road safety with patients' rights​.”

Cannabis And Vehicle Operation Laws In Australia

Australia, like many other places, defines the presence of cannabis as impairment, which is the most extreme and archaic form of prohibition. Again, while nobody wants impaired drivers, THC presence at random road checks with a simple swab in the mouth cannot be a civilized approach. There is little to defend this position except an abundance of caution, which is hard to argue with given public safety parameters. As wrong as it is, the debate continues.

Australian contributor Elizabeth Warburton of Nativva notes: 

“...in Australia, cannabis is the only legally prescribed medication for which you lose your license when testing positive for presence. Australian laws do not account for the difference between presence and impairment, making medicinal cannabis inaccessible to Australians who require the ability to drive in their everyday lives. Current driving laws are prohibitive and discriminatory, as penalties for testing positive for cannabis are more severe than the penalties faced by drivers with a positive breath test for alcohol. These laws mean patients cannot even take a full-spectrum oil with minimal amounts of THC without fear of losing their license and livelihood, which is impeding positive health outcomes nationwide.” 

Contributor Fadi Roumieh adds:

“Medical cannabis patients report significant improvements across various health-related quality-of-life measures and an increase in function over time. A recent open-label trial produced positive results in simulated and perceived driving performance in patients on medicinal cannabis. The study suggested a negligible impact on driving performance. Further, government-funded trials are ongoing which aim to strengthen the case to change the driving laws in Australia.

The Future Of Cannabis And Driving Laws

While the debate continues around the globe, we can be certain that THC presence alone, measured by a mouth swab, is insufficient to gauge intoxication without other concrete impairment guidance to avoid unfair subjectivity. Levels of cannabis in the system alone may not take into consideration the medical needs and tolerance of individuals. Nobody wants impaired drivers on the road, so we must develop regulations to protect both public safety and patients’ rights.