Aussie drink-driving laws have similar penalties, but our BAC level is still at .05. This will be moved to .02 in the coming years. Be safe for you, your family and the person you may injure because, you thought you were ‘ok to drive!’
SHOULD YOU BE DRIVING? DON'T DRINK AND DRIVE....EVER!
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?
Devastating new research from the American College of Surgeons has exposed the lethal consequences of cannabis-impaired driving, revealing that more than 40% of drivers killed in car crashes between 2019 and 2024 in Ohio tested positive for high levels of THC.
Moreover, the findings, released last week, shatter the persistent myth that cannabis is a harmless substance with no fatal consequences. Indeed, the data adds to mounting evidence that driving under the influence of marijuana poses a severe and growing threat to road safety across the United States.
Federal Data Confirms Rising Threat of Drug-Impaired Driving
Significantly, the Ohio study aligns with multiple federal investigations documenting the escalating danger of cannabis-impaired driving on American roads. For instance, a 2022 study by the National Traffic Safety Board found marijuana present in approximately one-third of all motorists arrested for impaired driving nationwide.
Furthermore, research from the National Highway Traffic Safety Administration that same year revealed that over 25% of individuals killed or seriously injured in road accidents who tested positive for any drug had used marijuana. Remarkably, this figure exceeded the 23% who tested positive for alcohol, therefore signalling a fundamental shift in road safety threats.
Perhaps most alarming is the widespread misunderstanding amongst cannabis users about the drug’s effects on driving ability. Consequently, a survey conducted by the Foundation for Traffic Safety earlier this year questioned 2,000 cannabis users, uncovering troubling attitudes towards drug-impaired driving.
Specifically, the research found that nearly 85% of cannabis users drive on the same day they consume marijuana. More concerningly, 81% believe that using cannabis either has no effect on their driving or actually improves it, a misconception with potentially fatal consequences.
In Virginia, for example, approximately 17% of residents admitted to driving whilst high multiple times in the previous month, according to the state Cannabis Control Authority. In other words, that equates to nearly one in five people regularly operating vehicles whilst under the influence. Disturbingly, 30% of respondents believe cannabis users are usually safe drivers.
State-Level Evidence Links Legalisation to Increased Fatalities
Meanwhile, data from states that have legalised recreational cannabis reveals a disturbing pattern. Notably, Washington state witnessed the proportion of drivers involved in fatal collisions who tested positive for THC double after legalisation, from approximately 9% on average in the five years before legalisation to 18% in the subsequent five years.
Similarly, Colorado, an early adopter of cannabis legalisation in 2014, experienced a near doubling of cannabis-related car crash fatalities between 2013 and 2020. Following legalisation in Oregon, Alaska, and California, car crash deaths increased by 22%, 20%, and 14% respectively.
As a result, these statistics suggest that legalisation contributes to increased cannabis-impaired driving incidents, thereby undermining road safety gains achieved through decades of public health initiatives.
The Erosion of Road Safety Culture
Over several decades, America developed a powerful cultural taboo against drink-driving, largely through sustained education and prevention campaigns by organisations such as Mothers Against Drunk Driving (MADD). Subsequently, these efforts fundamentally changed public attitudes and behaviours, saving countless lives.
However, the data indicates that cannabis legalisation has eroded similar taboos against drug-impaired driving. In particular, industry marketing campaigns promoting cannabis as medically beneficial and harmless have contributed to dangerous misperceptions about the drug’s effects on driving ability.
Additionally, the parallels with historic tobacco industry tactics are striking. Decades ago, tobacco companies paid medical professionals and scientists to promote cigarettes as beneficial to health. Today, the cannabis industry employs sophisticated marketing strategies that downplay or ignore the substance’s well-documented risks.
Broader Health Concerns Beyond Road Safety
Nevertheless, the dangers of cannabis extend well beyond impaired driving. Recent studies have linked marijuana use to serious cardiac events, damaged fertility in women, schizophrenia, and other severe mental health conditions. Furthermore, high-profile incidents involving individuals with documented cannabis use have highlighted the drug’s potential connection to violent behaviour.
Consequently, these broader health implications underscore the need for comprehensive approaches to cannabis prevention that address both immediate risks like cannabis-impaired driving and long-term health consequences.
Urgent Need for Prevention and Education
Clearly, the escalating crisis of drug-impaired driving demands immediate action. Therefore, robust awareness and prevention programmes are essential to educate the public, particularly younger drivers, about the deadly dangers of operating vehicles whilst under the influence of cannabis.
In addition, states must reconsider policies that have normalised cannabis use without adequate safeguards or public health protections. Indeed, the rush to legalisation has outpaced understanding of the substance’s risks, thus creating preventable tragedies on roads across the nation.
Moreover, federal authorities should prioritise research into cannabis-impaired driving, develop evidence-based prevention strategies, and support states in implementing effective enforcement and education measures. Ultimately, public health campaigns must counter industry messaging and establish clear understanding that cannabis significantly impairs driving ability.
In conclusion, the evidence is unequivocal: cannabis-impaired driving represents a growing threat to public safety. Only through comprehensive prevention efforts, honest public education, and evidence-based policy can this escalating crisis be addressed effectively.
A comprehensive decade-long study examining drug and alcohol presence in Victorian road crashes has revealed alarming trends, with methylamphetamine emerging as the most prevalent illicit substance detected in both injured and fatally injured drivers between 2010 and 2019.
The research, published in Injury Prevention and led by Monash University, represents the largest investigation of its kind conducted in Australia. Analysing data from 19,843 injured drivers and 1,596 fatalities, the findings paint a concerning picture of drug-impaired driving across Victoria’s roads.
Methylamphetamine Prevalence in Road Crashes Reaches Alarming Levels
The study found that methylamphetamine had the highest prevalence among Victorian drivers involved in crashes. Researchers detected the substance in 12.3% of fatalities and 9.1% of injured drivers, and these detections increased over time.
Taken together, these statistics underscore a growing public health and road safety challenge. In particular, methylamphetamine impairs cognitive function, reaction times, and decision-making abilities, all of which are critical for safe vehicle operation.
Multiple Substances Detected in Victorian Drivers
The research revealed that 16.8% of car drivers and motorcyclists tested positive for one or more drugs. Alcohol remained a significant factor, with 14% of crashes involving a blood alcohol concentration (BAC) at or exceeding 0.05%.
Cannabis (THC) emerged as another substance of concern, with detections rising amongst injured drivers until 2018. The study found THC detected in 8.1% of injured drivers and 15.2% of fatally injured drivers.
MDMA-positive driving decreased amongst injured drivers and remained stable at approximately 1% of fatalities throughout the study period.
Drug-Driving Patterns in Motorcyclists
Motorcyclists emerged as a particularly vulnerable population. Between 2015 and 2019, methylamphetamine was detected in 27.9% of motorcyclist fatalities, a figure substantially higher than the overall driver population. THC followed at 18.3%, with alcohol at or above 0.05% BAC detected in 14.2% of fatal motorcycle crashes. Similar but lower frequencies were observed amongst injured motorcyclists.
These elevated rates amongst motorcyclists warrant particular attention, as riders already face heightened vulnerability on roads due to reduced physical protection compared to enclosed vehicle occupants.
Alcohol Trends Show Mixed Results
The study documented a decline in alcohol detections (≥0.05% BAC) amongst fatalities. However, alcohol detections increased amongst injured motorcyclists and car drivers until plateauing in 2017. This mixed trend suggests that whilst fatal alcohol-related crashes may be decreasing, alcohol continues to contribute significantly to road trauma overall.
Demographics and Risk Factors
The research identified that there was a higher incidence of drug-positive driving amongst men and individuals aged between 25 and 59 years, alongside patterns of increasing drug use in motorcyclists.
Implications for Road Safety Prevention
The comprehensive data from the Victorian Institute of Forensic Medicine and Victoria Police provides robust evidence of persistent drug-impaired driving despite Victoria’s enhanced road safety measures.
Co-senior author Adjunct Associate Professor Dimitri Gerostamoulos from Monash University’s Department of Forensic Medicine and the Victorian Institute of Forensic Medicine stated that the findings confirm methylamphetamine, alcohol, and cannabis are the drugs that cause the most harm on Victorian roads.
The decade-long trends demonstrate that current prevention strategies require re-evaluation and strengthening. The study’s authors concluded that despite enhanced road safety measures in Victoria, drug-driving persists, indicating a need for revised prevention strategies targeting this growing issue.
Addressing the Drug-Driving Challenge
This research provides critical baseline data for policymakers, law enforcement, and public health officials working to reduce drug-driving incidents. The upward trajectory of methylamphetamine detections, combined with persistent alcohol involvement and rising cannabis presence, indicates that impaired driving prevention must remain a priority.
Understanding which substances most frequently impair drivers, and which demographic groups exhibit highest risk, enables targeted prevention initiatives. The particularly high rates of drug detection amongst motorcyclists suggest this group requires specialised attention in prevention messaging and enforcement strategies.
As Victoria continues developing its road safety framework, this evidence base highlights where authorities should concentrate prevention efforts to achieve meaningful reductions in drug and alcohol-related road trauma.
Background Driving under the influence of alcohol and other drugs contributes significantly to road traffic crashes worldwide. This study explored trends of alcohol, methylamphetamine (MA), 3,4-methylenedioxy-N-methylamphetamine (MDMA) and Δ9-tetrahydrocannabinol (THC), in road crashes from 2010 to 2019 in Victoria, Australia.
Methods We conducted a cross-sectional analysis using data from the Victorian Institute of Forensic Medicine and Victoria Police, examining proscribed drug detections in road crashes. Time series graphs per substance explored indicative trends and comparisons between road users. Negative binomial regression models, with robust SEs and adjusted for exposure (kilometres travelled, Victorian licence holders), modelled the incidence rate ratio, with a Bonferroni-adjusted α=0.007 for multiple comparisons.
Results There were 19 843 injured drivers and 1596 fatally injured drivers. MA had the highest prevalence (12.3% of fatalities and 9.1% of injured drivers), demonstrating an increase over time. Overall, 16.8% of car drivers and motorcyclists tested positive for one or more drugs, with 14% of crashes involving a blood alcohol concentration (BAC)≥0.05%. MA and THC were the most common drugs in fatalities. Between 2015 and 2019, MA was detected in 27.9% of motorcyclist fatalities, followed by THC (18.3%) and alcohol ≥0.05% (14.2%), with similar but lower frequencies among injured motorcyclists. Alcohol detections (≥0.05% BAC) in fatalities declined, but increased in injured motorcyclists and car drivers until plateauing in 2017. THC detections rose among injured drivers until 2018, detected in 8.1% and 15.2% of injured and fatal drivers, respectively. MDMA-positive driving decreased among injured drivers and remained stable at ~1% of fatalities.
Conclusions Despite enhanced road safety measures in Victoria, drug-driving persists, indicating a need for revised prevention strategies targeting this growing issue.
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.
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.
The Scope of the Problem
The Ohio findings are far from an isolated incident. A 2022 study from the National Highway Traffic Safety Administration found that more than 25% of all those killed or seriously injured in road accidents who tested positive for any drug tested positive for marijuana, a higher rate than that found for alcohol at 23%. Even more alarming, a September 2024 study by researchers at London School of Economics found that the legalisation of recreational marijuana increased traffic fatalities by 75% in Alaska, 18% in California, 16% in Oregon, and 15% in Colorado.
The implications are staggering. Analysis from Harvard and New York Medical College researchers shows that if marijuana were legalised nationwide, the U.S. would suffer an additional 6,800 fatal crashes per year. These numbers represent real lives lost, families devastated, and communities forever changed by preventable tragedies.
Direct Impairment of Critical Driving Skills
Cannabis consumption significantly impairs multiple cognitive and motor functions essential for safe driving. Research has consistently demonstrated that marijuana use affects motor control and reaction time, with studies showing marijuana increases driver reaction time and the number of incorrect responses to emergencies. Users demonstrate difficulty maintaining consistent lane position and experience problems with speed variability. The ability to process multiple inputs simultaneously becomes compromised, affecting divided attention and attention maintenance capabilities that drivers rely upon constantly.
Executive function deteriorates under the influence of THC, affecting route planning and judgment in ways that can have fatal consequences. Perhaps most concerning, recent research reveals that cannabis has significant adverse effects on visual acuity, contrast sensitivity, stereoacuity, and causes night-vision disturbances. Laboratory studies examining the impairment effects of marijuana use on psychomotor and cognitive functions have shown that cannabis consumption can impair driving task-related abilities such as motor control, executive function, visual processing, short-term memory, and working memory in a dose-dependent fashion.
Reviews of studies on the effects of marijuana on driving skills have demonstrated that marijuana specifically impairs certain skills necessary for safe driving. These include controlling speed variability, maintaining proper lane positioning, sustaining adequate reaction time, managing divided attention, maintaining attention over time, planning routes effectively, making sound decisions, and properly assessing risks. In some driving simulator studies, marijuana use increased driver reaction time and the number of incorrect responses to emergencies. Drivers crashed more frequently into sudden obstacles when on high doses of THC, though this effect was not observed at lower doses.
Demonstrable Increase in Crash Risk
The crash risk data leaves no doubt. Multiple studies have shown that marijuana use increases the risk of fatal crash involvement, with drivers facing injury risk between 1.8 and 2.8 times higher than non-users. Research on drivers in fatal crashes has shown that THC-positive drivers were more than twice as likely to crash as drivers without THC in their system. The odds of drivers being found responsible for a crash increase substantially with rising marijuana concentrations in the blood.
At very high THC levels, the odds ratio for crashes can reach 10.0, representing an extraordinarily elevated risk. Studies investigating cannabis use as a risk factor for motor vehicle crash fatalities have found that while the degree of impairment varies by tetrahydrocannabinol level, the association between cannabis use and significantly increased risk of fatal crash involvement remains consistent across research. Meta-analyses confirm that acute THC administration impairs aspects of driving performance in measurable and significant ways.
The results are devastating
Dangerous THC Concentration Levels
The Ohio data revealed extremely high THC levels among deceased drivers, averaging 30.7 ng/ml. Impairment thresholds typically fall around 2-5 ng/ml, meaning these drivers had concentrations more than six times higher than levels associated with significant impairment. These elevated concentrations indicate recent use before driving and demonstrate a complete disregard for impairment risks. The data suggest an absence of effective deterrence or awareness and point to a potential normalisation of drugged driving behaviour that should alarm anyone concerned with public safety.
Colorado’s Department of Public Health and Environment examined driving impairment and motor vehicle crash risk relative to marijuana use, and evidence indicating how long it takes for impairment to resolve after marijuana use. Their findings confirmed that the risk of a motor vehicle crash increases among drivers with recent marijuana use. Using alcohol and marijuana together increases impairment and the risk of a motor vehicle crash more than using either substance alone. For less-than-weekly marijuana users, using marijuana containing 10 milligrams or more of THC is likely to impair the ability to safely drive, bike, or perform other safety-sensitive activities.
The Post-Legalisation Effect
Evidence from jurisdictions with experience in cannabis legalisation tells a cautionary tale that policymakers ignore at their peril. In Washington State, researchers assessed cannabis involvement and THC levels among fatally injured drivers before and after legalising non-medical cannabis use. Using data from all motor vehicle crash decedent drivers based on observed and imputed values, the prevalence of cannabis involvement in fatalities was 9% prior to legalisation and 19% after. In adjusted analyses, the proportion of decedent drivers with high THC levels (greater than 10 ng/ml) increased nearly five-fold after legalisation.
Although cannabis testing rates increased during the study period, findings remained generally similar when restricted to those with completed cannabis testing. This study was one of the first to impute cannabis involvement in motor vehicle crash fatalities among decedents without testing and to measure and impute THC levels rather than simply the presence or absence of THC. The results add to literature suggesting that legalising cannabis may increase motor vehicle crash fatalities and highlight the need to better characterise and mitigate those risks.
Colorado’s experience has been similarly troubling. The state’s Division of Criminal Justice analysed driving under the influence case filings and found that among cases with cannabinoid screens, 66% tested positive for cannabinoids, with 57% of all screened cases testing positive for Delta 9-THC specifically. The median value of Delta 9-THC among individuals screened was 5.2 ng/mL and the mean was 8.2 ng/mL, both of which exceeded the permissible inference level. About half of the case filings with Delta 9-THC confirmation tests had levels at or above the permissible inference level of 5 ng/mL.
The Myth of Compensatory Behavior
While some studies have suggested that marijuana users may adopt compensatory behaviours like driving slower or maintaining greater following distances, this finding creates a misleading impression of safety. Simulator studies investigating behavioural changes when driving under the influence of marijuana have concluded that marijuana use by drivers may cause decreased speeds, fewer attempts to overtake, and increased following distance to the vehicle in front. These findings stand in sharp contrast to studies investigating the effects of alcohol use.
However, these behaviours do not eliminate the fundamental impairment caused by cannabis use. They merely reflect user awareness of diminished capacity. Recent research shows that users’ perception of when impairment has resolved often occurs before actual driving performance improves. One study measuring driver performance in a simulator showed subjects perceived the impairing effects of THC to be eliminated before a measurable improvement in driving performance was seen. The false sense of security created by perceived compensation can itself be dangerous, as drivers may believe they are driving safely when objective measures show continued impairment.
Furthermore, compensatory behaviours do not prevent the fundamental cognitive and motor impairments that increase crash risk. Studies have shown that despite potentially driving more slowly, marijuana-impaired drivers still hit more pedestrians, exceed speed limits more often, make fewer stops at red lights, and make more centreline crossings than sober drivers. The notion that slower driving compensates for impairment ignores the reality that safe driving requires far more than speed control.
The Myth of Tolerance
Cannabis advocates often claim that regular users develop tolerance to impairing effects, making them safer drivers than occasional users. Evidence strongly contradicts this. While some tolerance to THC’s effects may develop, it does not eliminate impairment or reduce crash risk. In reality, as tolerance builds, users tend to increase their dose to reach the same psychoactive effects—a pattern well documented in both research and clinical settings. This makes the supposed safety benefit of tolerance an illusion, as users simply consume more to overcome reduced sensitivity. Studies comparing occasional and daily cannabis users found that both groups showed significant driving impairment. Although daily users drove slower, this compensatory behaviour failed to remove measurable performance deficits.
Chronic Impairment and False Comparisons
Regular users may also experience chronic impairment due to THC’s fat-soluble nature, which allows it to linger in brain tissue. The body continues to release and metabolise this residual THC, sometimes converting it into 11-hydroxy-THC—an even more intoxicating compound. This ongoing effect undermines claims that frequent users are safer. Similar arguments were once made about alcohol tolerance, with drinkers claiming experience made them safer drivers. Society rightly rejected that logic when setting drunk driving laws. The same principle applies to cannabis: impairment remains impairment, regardless of tolerance, and driving under its influence poses an unacceptable risk (Source: WRD News)
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The National Alliance for Action on Alcohol is a national coalition of health and community organisations from across Australia that has been formed with the goal of reducing alcohol-related harm.
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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?
Devastating new research from the American College of Surgeons has exposed the lethal consequences of cannabis-impaired driving, revealing that more than 40% of drivers killed in car crashes between 2019 and 2024 in Ohio tested positive for high levels of THC.
A comprehensive decade-long study examining drug and alcohol presence in Victorian road crashes has revealed alarming trends, with methylamphetamine emerging as the most prevalent illicit substance detected in both injured and fatally injured drivers between 2010 and 2019.
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.
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.
