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Driving Under the Influence of Marijuana: More Dangerous Than You Think!

After decades of public and private campaigns to educate the public about the dangers of driving while under the influence of alcohol, it’s safe to say that every driver in America should know that drinking and driving don’t mix. At the same time, however, there have often been contradictory reports about potential dangers associated with driving while under the influence of marijuana. After all, marijuana advocated have been claiming for years that their drug of choice is much safer than alcohol, and many have suggested that drugged driving is relatively safe too. The facts, however, indicate that the combination of marijuana use and driving is more dangerous than many people believe.

The NHTSA Studies

In 2014, the National Highway Traffic Safety Administration conducted a study to compare the dangers associated with both drugged driving and drunk driving. That study suggested that the use of marijuana by drivers did, in fact, represent a much lower crash risk than drinking and driving. According to the study, the presence of THC in a driver’s system did not correlate with any statistically noticeable change when it came to increasing the risk that drivers might crash. Meanwhile, alcohol appeared to create a seven-fold increase in that crash risk.

thc-quoteHowever, it should be noted that such testing may not tell the whole story. Science tells us that THC can remain in the body for days and weeks after marijuana use and that its depletion is far less predictable than the rate at which alcohol levels decrease. What does that mean? Put simply, any tests that seek to identify a correlation between THC levels and crash rates are inherently unreliable, since the presence of THC does not necessarily mean that the driver is still under the influence of the drug.

Some might think that this doesn’t really matter – that you’re either impaired or not impaired, regardless of what the THC tests might show. On a certain level, that is correct. The real issue with marijuana use – as it is with drinking and driving – is whether the driver is impaired. The problem is that marijuana has thus far proven difficult to track when it comes to impairment. And since the NHTSA’s research into this issue has also identified an increase in the number of drivers testing positive for the drug in night stops as a result of the trend toward legalization in some states, the matter clearly needs to be addressed. 

But Does Marijuana Impair Driving Skills?


Contrary to what many cannabis advocates claim, there is scientific evidence that demonstrates that marijuana use can seriously impair driving skills. In one study that directly addressed the subject, researchers concluded that the risk of being in an accident after smoking cannabis is doubled. The study noted the increased risk in those who had elevated THC levels in their blood, while acknowledging other research that found no increased risk when only urine samples were used to test those levels. This study was notable for focusing attention on those who had recently smoked cannabis, rather than relying on test subjects who simply had TBC in their systems.

Researchers found that drivers were impaired in a number of ways:

  • Reaction times were affected
  • Many drivers slowed their vehicles to compensate for their impairment
  • They veered into other lanes more frequently
  • They failed tests involving critical tracking – tests that assess distraction levels
  • Many demonstrated impaired cognitive function

The Numbers Are Alarming

fatal-accidents-statsIn addition to scientific studies, there is also growing statistical evidence that marijuana impairment is a serious concern. For example, about 7% of drivers involved in fatal automobile accidents are found to have THC in their systems. The problem could be even worse with our younger drivers, as a generation of teenagers seem to be growing up under the delusion that marijuana either has no impact on driving skills or – and hold on to your seat for this one – actually makes you a better driver! That’s from a 2013 survey of teen drivers, in which 34% of those youngsters actually said that they believed marijuana improves driving skills. Another 41% asserted that it had no impact on driving.


Those perceptions matter too, especially when you consider that the CDC has identified automobile crashes as the number one cause for teen deaths, with thousands of teens dying each year on the nation’s roads and highways, and many tens of thousands more suffering injuries. If the nation’s teens are growing up with the belief that they can use marijuana and drive without increasing their risk of being in a crash, those numbers may look even worse in the decades to come.

What Cannabis Proponents Claim

It is interesting to note that many of the groups committed to legalizing cannabis everywhere take issue with the studies that indicate driving impairment, and even minimize the actual risks. NORML, for example, chooses to minimize the types of impairment that have been identified – swerving into other lanes and reduced reaction times, for example – by citing researchers who suggest that such impairments don’t necessarily affect performance.

The fact is, however, that an inability to remain in your own lane is a performance failure by any objective standard. It’s one of the first things we teach young drivers: stay in your lane unless you’re intentionally changing lanes. As for the notion that reduced reaction times are not indicative of impairment of performance, that too is absurd. If THC causes slow reaction times, that is impairment and can lead to poor driving performance.

The Bottom Line

Marijuana advocates are free to argue in favor of legalization of their favorite drug and can claim that THC is harmless when it comes to drivers. They have that right. Logic, and the weight of scientific evidence and traffic studies, however, tell a different story. Facts are stubborn things, after all. And what the facts suggest in this instance is that drugged driving puts drivers and others on the road at increased risk of crashes that can cause injury or even death.