Does Cannabis Impair Driving Long After the High is Gone?

Matt Weeks February 26, 2020 0 comments

Is a person’s driving affected by cannabis consumption? Yes, but not in the way you might think.

New research published in the Journal of Drug and Alcohol Dependence (2020) asks society to reconsider the relationship between smoking weed and operating an automobile. For years, the accepted wisdom was that acute cannabis intoxication slowed reaction times and made drivers less safe. The new science, however, suggests that while cannabis does impair driving, but also that there are others factors to consider.

Instead of focusing on current intoxication, the researchers examined sober drivers who regularly consumed cannabis. In other words, they tested drivers who consume cannabis regularly but were not under the influence of THC at the time of the driving simulation. The goal was to find out if cannabis could blunt driving abilities long after it had ceased to produce intoxicating effects.

Using a driving simulator, the scientists found a direct association between poor driving skills and people who started consuming cannabis before the age of 16. Interestingly, the research discovered it to be a significant predictor of poor driving when compared to heavy consumers who began at a later age.

What Does This Mean? How Does Cannabis Impair Driving?

It’s important to contextualize these new findings within the current understanding of the question: “Does cannabis impair driving?”

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No research exists in a vacuum, and far from overturning previous data, the new data helps fine-tune the scientific position on consuming cannabis while using a car. What it doesn’t do, however, is provide proof that cannabis consumption makes people worse drivers. But, it does suggest that this could be the case for drivers who began to experiment with cannabis before age 16.

The other chronic cannabis consumers — the ones who began after age 16 — fared no differently than the control group. Interestingly, the poor test-driving skills happened only to recreational cannabis consumers. However, if someone asked, “Does cannabis impair driving in medical patients?” The answer would be a resounding no.

The researchers found, contrary to expectations, medical cannabis patients had improved driving abilities after taking their cannabis prescriptions.

DOES CANNABIS IMPAIR DRIVING might be what this young woman smoking a joint on a bridge should be thinking of

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What the Study Missed

The researchers may be on to something about drivers who began consuming cannabis early. It could be that cannabis affects the motor skill refinement in developing brains to the point that young consumers become permanently sub-par drivers. But that’s not what this study proved.

It proved there is a correlation between early cannabis consumption and poor performance on a driving simulator. It did not demonstrate causation. That’s an important distinction.

It’s possible that early cannabis consumption is responsible for poor driving skills later in life, but it’s just as possible that another variable exists. Perhaps the same impulsivity that leads 15-year-olds to experiment with an intoxicating substance also makes them rash drivers.

It’s also possible that 15-year-olds who turn to cannabis do so because they’re self-medicating a different kind of motor or focus problem but lack the resources to effectively identify it. That same problem, exacerbated and perhaps ill-treated for years, could account for sub-par automobile operation as well. It could also be that early cannabis consumers fare worse on driving simulators but perform well on the actual road.

Whatever the case, the new research is interesting. But it’s not enough to answer the question “Does cannabis impair driving abilities in people who are not under its influence?” in the affirmative.

Other Factors that Impair Driving

While it would be easy to blame a single variable on poor motoring skills, it’s probably much more complicated than that. The likelihood that cannabis alone is not responsible for bad driving is further evidenced by other scientific research.

A raft of studies shows that early-onset cannabis consumption is associated with poor cognitive performance throughout life. Those studies include this one, published in the Journal of Psychoactive Drugs (2011); another one published in the International Review of Psychiatry (2018); and this research from Frontiers in Psychiatry (2013).

Again, there is no proof that cannabis alters brain cells or destroys neural links. It could be the kind of people who turn to cannabis very early (for non-medical reasons) have already damaged their neural functions.

Don’t forget that while cannabis can lead to impaired driving (especially in young people), it’s nothing compared to alcohol. A study published in Addiction (2005) found that once other variables, such as blood alcohol level, are controlled for, cannabis no longer significantly impacts the odds of collision.

In other words, cannabis is not really to blame for car wrecks unless it’s combined with other substances.

DOES CANNABIS IMPAIR DRIVING might be what these hands rolling ablunt need to think of

Early Onset Cannabis Consumption: The Real Stuff

A bevy of complimentary data on the poor cognitive performances of early onset cannabis consumers seems to point toward a consensus understanding that recreational cannabis consumption too early in life may lead to trouble down there road.

All of these studies ca, of course, be explained by other variables, but it’s also just as likely that consuming cannabis during critical periods of brain development has consequences that science cannot fully articulate yet.

For the purposes of safety and health, it’s best to keep cannabis away from children and young teenagers until science can better sort out what cannabis does to developing brains or what causes troubled youngsters to turn to cannabis in the first place.


Dahlgren, M. et al. (2020) Recreational cannabis use impairs driving performance in the absence of acute intoxication. Drug and Alcohol Dependence. 107771: https://doi.org/10.1016/j.drugalcdep.2019.107771
Anderson, Beth. Et al. (2010) Sex Differences in the Effects of Marijuana on Simulated Driving Performance. Journal of Psychoactive Drugs. 42:1, 19-30, DOI: 10.1080/02791072.2010.10399782
Kelly A. Sagar & Staci A. Gruber (2018) Marijuana matters: reviewing the impact of marijuana on cognition, brain structure and function, & exploring policy implications and barriers to research. International Review of Psychiatry. 30:3, 251-267, DOI: 10.1080/09540261.2018.1460334
Lisdahl, Krista M. et al. (2013) Dare to delay? The impacts of adolescent alcohol and marijuana use onset on cognition, brain structure, and function. Frontiers in Psychiatry. 01 July 2013: https://doi.org/10.3389/fpsyt.2013.00053
Blows, Stephanie et al. (2005). Marijuana use and car crash injury. Addiction vol 100, 5: https://doi.org/10.1111/j.1360-0443.2005.01100.x
Author avatar

Matt Weeks

A writer living and working in Athens, GA, Matt's work has appeared in various newspapers, books, magazines and online publications over the last 15 years. When he's not writing, he hosts bar trivia, plays in local bands, and makes a mean guacamole. He holds an undergraduate degree in journalism and a master's degree in organizational theory. His favorite movie is "Fletch."

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