Imagine if you had to tell a family that their child was never coming home again...because a driver had a few too many drinks and they were too lazy to get a taxi? How would you feel if it was your child? Your brother, your parent, your best friend? Now imagine that you're the one who had a few drinks and thought...Home isn't too far. I'll make it without getting busted. While on the back streets worrying if the booze bus will catch you, you hit someone. How do you live with that for the rest of your life?Unique Pharmacological Challenges
Unlike alcohol, which displays a relatively predictable concentration-response relationship, THC presents distinct challenges for measuring and predicting impairment. THC is highly fat-soluble, leading to unpredictable absorption, distribution, and elimination patterns that vary significantly among individuals and circumstances. Peak THC concentrations do not correlate well with the degree of behavioural impairment, meaning that blood levels alone cannot reliably indicate driving fitness.
Studies on marijuana use and driving impairment have shown that the level of THC measured in blood or oral fluid and the degree of impairment are not closely related. Peak THC levels can occur when low levels of impairment are measured, and high levels of impairment can be measured when THC levels are low. This disconnect occurs because the hydrophobic THC molecule rapidly leaves hydrophilic blood as THC distributes readily into the brain and fatty tissue. Studies have shown very low THC blood levels of 2-4 ng/ml within one to two hours of use, even while significant impairment persists.
The route of administration dramatically affects onset and duration of effects. If marijuana is ingested through edibles, the onset of impairing effects occurs more slowly and lasts longer compared to smoking. Oral THC may take two to three hours to reach peak blood levels, meaning that someone could be significantly impaired immediately after consumption while still registering extremely low blood concentrations. Conversely, smoked marijuana produces rapid onset of effects with peak impairment occurring relatively quickly.
Individual biological factors create wide variability in response to THC. Absorption, distribution, and elimination vary based on route and frequency of intake, THC dose, titration of dose when smoked or vaporised, and individual user characteristics including body composition, metabolism, and genetic factors. These factors affect not only the amount of marijuana intake and metabolism but also the degree of behavioural impairment exhibited by users. The lack of definitive knowledge to quantify a concentration-response relationship for marijuana may be in part due to typical differences in research methods, tasks, subjects, and dosing that have been used to date.
Lack of Awareness Among Users
Perhaps most disturbing is the evidence of widespread ignorance about cannabis-related driving risks. The Ohio data showed THC levels indicating very recent use, suggesting drivers felt no hesitation about operating vehicles while impaired. Research consistently shows a considerable proportion of cannabis users have driven after using the drug, often with little concern about the risks they pose to themselves and others. Many users underestimate or remain completely unaware of the visual impairment caused by cannabis.
Normalising cannabis use has reduced perceived risks in the minds of many users. Prevention professionals understand that legalisation of substances lowers an individual’s perception of risk, altering judgment about the likelihood of negative occurrences related to that substance. As jurisdictions expand marijuana legalisation, the perception that cannabis use is benign extends to assumptions about driving while impaired. According to the National Highway Traffic Safety Administration, there has been a 48% increase in nighttime drivers who tested positive for THC, the chemical responsible for marijuana’s psychological effects.
According to the Traffic Safety Culture Index, drivers who use both marijuana and alcohol were significantly more prone to driving under the influence of alcohol. They are more likely to speed, text, intentionally run red lights, and drive aggressively. In 2020, SAMHSA data showed that around 12.6 million people ages 16 and up drove after using drugs, with the vast majority of nearly 12 million under the influence of marijuana. These numbers reveal a catastrophic failure of public awareness and prevention efforts.
Mental and Visual Acuity Utterly Undone
Visual Impairment Without User Awareness
Recent breakthrough research has revealed a particularly dangerous phenomenon that should concern everyone who shares the road. Cannabis significantly impairs visual function, but users often remain completely unaware of this impairment. A comprehensive study analysing the effects of smoking cannabis on vision found significant adverse effects on static visual acuity, contrast sensitivity, stereoacuity, accommodative response, straylight, night-vision disturbances (halos), and pupil size. All these parameters showed statistically significant impairment after cannabis use.
The study’s findings on self-perceived visual quality revealed that about two-thirds of participants thought using cannabis impaired their vision. This means approximately one-third of users did not perceive their vision had worsened after using cannabis, despite measurable deterioration in multiple visual parameters. This lack of awareness creates dangerous false confidence in driving ability. Contrast sensitivity, specifically for the spatial frequency of 18 cycles per degree, was identified as the only visual parameter significantly associated with self-perceived visual quality.
Cannabis consumption has a negative effect on both visual function and driving performance. The impairment noted in driving performance could be substantially due to visual degradation, given that most of the integrated information for driving is captured by the visual system. The research found significant correlations between certain visual and driving performance parameters, particularly regarding driving stability. The results highlight the importance of parameters such as visual acuity, contrast sensitivity, and stereoacuity, which play key roles in maintaining the vehicle in the lane properly.
The researchers noted that their results suggest a considerable lack of awareness of the risks associated with cannabis use in driving, given that a considerable proportion of participants had driven after using cannabis. They emphasised the need for awareness-raising and information campaigns aimed at the citizens, and continued research providing adequate insights into how this drug affects both short-term and long-term vision and the ability to drive safely.
The “Medicinal Cannabis” Exemption: A Public Safety Risk
Currently, significant lobbying pressure exists to exempt “medicinal” cannabis users from drugged driving laws. Proponents argue that treating their prescribed medication differently from other pharmaceutical preparations creates unfairness in the legislation. Those using cannabis formulations believe they are unfairly penalised compared to users of other prescription medications. This proposal presents several critical problems that make it unacceptable from a public safety perspective.
The presence of THC as the psychotropic constituent of cannabis-based drugs impairs driving skills regardless of whether it was obtained through prescription or recreational channels. The source of THC is irrelevant to its impairing effects on the brain and body. Many properly vetted and approved prescribed pharmaceutical grade medications of various origins can create impairment via drowsiness, and slower reaction times this diminished state can bring. Consequently, these prescriptions come with clear warnings that driving while on this medicine is warned against.
However, THC-induced intoxication represents a fundamentally different state from simple drowsiness. Intoxication brings another level of diminished capacity to the driver. Along with the idiosyncratic nature of intoxicants including THC, the potential for multi-level public harms is markedly increased. Drowsiness can be one symptom of intoxication, but intoxication involves far more than drowsiness alone. The comprehensive impairment of cognitive function, motor control, visual processing, and judgment that accompanies THC intoxication cannot be compared to the side effects of typical prescription medications.
Law enforcement cannot determine the source of THC detected in a driver’s system. Supplementing and misuse of cannabis products will be made substantially easier if medicinal exemptions are created. The potential for intoxicated driving to be given a free pass on the basis of claiming medicinal use becomes an obvious loophole that will be exploited. Under the current Pharmaceutical Benefits Scheme in Australia, the TGA certifies only two THC-based preparations as medicines: Sativex and Marinol. Other proposed formulations have not been fully subjected to clinical double-blind, placebo-controlled trials and have not been given pharmaceutical status. Scientifically, these products are not medicines.
The Australian Therapeutic Goods Administration has allowed and actively promoted a new category for “medicinal cannabis,” exponentially increasing the number of THC-contained products. Making the now Category 4 and 5 non-clinically trialled products easier to access for prescribing purposes has substantially grown the potential for abuse. How will law enforcement distinguish between THC from a prescription and THC from illicit sources? The answer is they cannot, rendering enforcement of drugged driving laws nearly impossible if exemptions are granted.
Insufficient Wait Times
Evidence suggests that even conservative estimates of safe waiting periods prove inadequate for ensuring driving safety after cannabis use. Colorado’s Department of Public Health and Environment made recommendations around marijuana use and driving based on extensive evidence review. For less-than-weekly marijuana users, they concluded that waiting at least six hours after smoking or eight hours after eating or drinking marijuana allows time for impairment to resolve. However, these recommendations reveal a critical problem: someone using THC daily would never have a safe window to drive.
If a baseline is drawn to maximise safety at 24 hours, then someone using this psychotropic substance daily will not be permitted to drive with any degree of assured safety. Even a 12-hour waiting period presents clear issues for regular users. The rapid distribution of THC into fatty tissues, including the brain, means blood levels drop while impairment may persist. Research is lacking on marijuana and impairment in frequent marijuana users, making it impossible to establish truly safe waiting periods for this population.
Recent research showing visual impairment and driving performance deficits extending beyond perceived recovery times raises serious questions about any proposed safe waiting period. One study found that subjects perceived the impairing effects of THC to be eliminated before a measurable improvement in driving performance was seen. The most recent research found that most driving-related skills are predicted to recover within approximately five hours, with almost all within approximately seven hours of inhaling 20 mg THC. However, oral THC-induced impairment may take longer to subside, and these estimates assume single-use by occasional users.
Limited Pharmaceutical-Grade Options
The expansion of what qualifies as medicinal cannabis has created a system ripe for abuse. Under the Australian Pharmaceutical Benefits Scheme, the TGA certifies only two THC-based preparations as medicines: Sativex and Marinol. These products have undergone rigorous clinical trials and received pharmaceutical status based on scientific evidence. Other proposed formulations have not been fully subjected to clinical double-blind, placebo-controlled trials. In scientific terms, these products lack the evidence base to be classified as medicines.
The Australian Therapeutic Goods Administration now actively promotes a new category for medicinal cannabis, exponentially increasing the number of THC-containing products available. Making Category 4 and 5 non-clinically trialled products easier to access for prescribing purposes has substantially increased availability. The potential for abuse of this new opportunity to access cannabis legally has grown dramatically. Users can now obtain cannabis products through medical channels that have not been subjected to the rigorous testing required of traditional pharmaceuticals.
The distinction between pharmaceutical-grade medicines and these expanded cannabis products matters enormously for driving safety. Traditional medicines undergo extensive research to characterise their effects, appropriate dosing, side effects, and contraindications. Cannabis products entering the market under expanded medicinal frameworks lack this robust evidence base. Prescribers and users have limited guidance about appropriate use, and the products themselves vary widely in potency and composition.
The Need for Evidence-Based Policy
The evidence is overwhelming and consistent across multiple jurisdictions and research methodologies. Cannabis use significantly impairs driving ability and substantially increases crash risk. Any policy that would exempt cannabis users from drugged driving laws represents an unacceptable compromise of public safety, regardless of whether that use occurs under the banner of medicine or recreation.
Zero-tolerance laws must remain in place, keeping cannabis (THC) firmly within the prohibited substances category for driving. No medical exemptions should be granted, as the source of THC has no bearing on its impairing effects. Clear mandatory wait times must be established and enforced, with minimum periods of 24 hours or more between cannabis use and driving for those who use THC-containing products. These waiting periods need to account for the pharmacokinetic properties of THC and the mounting evidence showing that impairment persists long after blood levels have dropped.
Public education campaigns similar to those deployed against drunk driving need to be launched immediately. The success of Mothers Against Drunk Driving in transforming cultural attitudes about alcohol-impaired driving provides a proven model for addressing cannabis-impaired driving. These campaigns must counter the normalisation of cannabis use and clearly communicate the genuine risks of driving while impaired. They must also dismantle the widespread misconception that medicinal use somehow confers immunity from impairment, a notion as dangerous as the old belief that experienced drinkers could safely drive above legal alcohol limits.
Warning labels on THC-containing products require substantial strengthening. Current warnings about drowsiness fail to adequately communicate the full spectrum of impairment risks. Labels must clearly present crash data and explain the specific ways cannabis impairs driving, including effects on reaction time, visual processing, judgment, and motor control. Explicit prohibitions on driving after use need to be prominently displayed. The warnings should specify minimum waiting periods and acknowledge that regular users may face considerably longer periods before safe driving can resume.
Policymakers must actively resist the normalisation of cannabis use being promoted through industry-funded campaigns. The marijuana industry has employed slick, well-funded marketing to minimise perceived risks and maximise market penetration. These efforts directly undermine public safety by creating false impressions that cannabis use carries minimal consequences. Government messaging must counter these narratives with evidence-based information about real harms, including the documented increases in traffic fatalities following legalisation.
Law enforcement requires adequate training and resources for detecting and prosecuting drugged driving. Cannabis impairment presents unique detection challenges compared to alcohol, where breathalysers provide immediate roadside assessment tools. Officers need comprehensive training in recognising signs of THC impairment through standardised field sobriety tests and drug recognition protocols. Laboratory capacity must expand significantly to handle increased testing demand. Legal frameworks must support effective prosecution despite the pharmacokinetic complexities of THC, including the disconnect between blood levels and actual impairment that makes cases more challenging than traditional drunk driving prosecutions.
Conclusion
The journey to reduce drunk driving took decades of public education, legal reform, and cultural change. Society eventually reached consensus that operating a vehicle while impaired by alcohol posed unacceptable risk to public safety. That consensus translated into strict laws, rigorous enforcement, social stigma against drunk driving, and dramatic reductions in alcohol-related traffic fatalities. Cannabis-impaired driving demands similar commitment, but we cannot afford the same timeline. The evidence is already clear, the data already compelling, and the body count already mounting.
Cannabis consumption, whether labelled medicinal or recreational, has negative effects on visual function, cognitive processing, motor control, and driving performance. The impairment is real, measurable, and dangerous. The increase in crash fatalities following legalisation is documented across multiple jurisdictions including Washington, Colorado, Oregon, California, and Alaska. The public health crisis exists now, demanding immediate policy response.
Driving represents a privilege that comes with responsibilities to protect public safety. No therapeutic benefit of cannabis, real or perceived, justifies the risk of allowing impaired individuals to operate motor vehicles. Our communities worked too hard to address drunk driving to now enable a new generation of intoxicated drivers. Lessons learned from alcohol apply directly to cannabis. Impairment is impairment. Intoxication is intoxication. The specific substance matters less than the fundamental truth that diminished capacity behind the wheel kills people.
The data from Ohio, Colorado, Washington, Canada, and numerous other jurisdictions tell the same story with remarkable consistency. Cannabis and driving creates a deadly combination. Legalisation correlates with increased crash rates. Higher THC levels correlate with greater impairment and crash risk. Users frequently drive while impaired, often unaware of the full extent of their diminished capacity. The normalisation of cannabis use extends to dangerous acceptance of drugged driving.
Policymakers must listen to the evidence rather than industry lobbying. They must reject pressure to create medical exemptions that would gut drugged driving enforcement. They must prioritise the safety of all road users over the convenience of cannabis users. The alternative, measured in preventable deaths, catastrophic injuries, and families forever shattered by loss, is simply unacceptable. Every traffic fatality involving a THC-impaired driver represents a failure of policy and prevention that could have been avoided.
The Ohio data showing 40% of fatal crash drivers testing positive for THC should serve as a wake-up call. These deaths were preventable. These families could have been spared. These tragedies did not need to happen. Moving forward requires courage to enact and enforce policies that protect public safety even when those policies prove unpopular with cannabis advocates. The evidence demands action. The death toll demands response. The time for that response is now.
(Source: WRD News)
As jurisdictions worldwide continue to legalise cannabis for both “medicinal” and recreational use, a disturbing pattern has emerged on our roads. Recent data from Ohio revealing that over 40% of drivers killed in car crashes tested positive for THC represents just the latest confirmation of what extensive research has been warning us about for years: cannabis-impaired driving has become a critical public safety issue that demands immediate attention.
A tragic accident in Bexleyheath has shed new light on drug-driving risks as a bus driver, Martin Asolo-Agogua, pleaded guilty to causing the death of nine-year-old Ada Bicakci. The Bus driver cannabis death occurred when the driver, high on cannabis, struck Ada and her brother on Watling Street on the 3rd of August 2023. The heartbreaking incident resulted in Ada’s death two days later, while her younger brother survived the hit.
