A small number of states take these testing limitations into consideration and prosecutors have to prove impairment, regardless of how much THC is detected in a person’s system. Examples of acceptable evidence include erratic behavior, speech patterns, or the arresting offer’s testimony that they smelled cannabis in the vehicle (but that last one also raises the question of whether police can use it as an excuse to unlawfully search someone’s car).   

A newer method used to test for cannabis impairment behind the wheel, is check for blood-THC content. In the US, this is typically measured in nanograms per milliliter of blood, but there is no general standard and each state has their own limits. Some companies are also working to develop THC breathalyzers that can be utilized in the field.  

Cannabis DUI statistics  

It’s up for debate whether cannabis intoxication even has that much of an effect on driving at all. Although driving stoned can sometimes affect reaction times and peripheral vision, people typically compensate for these shortcomings by driving more carefully. 

That being said, some people really just do not drive well after using cannabis products and they should avoid doing it. What’s nice about these situations, is that people are can’t drive stoned usually avoid doing it anyway because it’s unpleasant and causes anxiety. When it comes to accidents involving only cannabis and no other substance, there is very little statistical data indicating that it’s as unsafe as driving drunk.  

For example, a 2010 study published in the American Journal on Addictions, which compared the effects of driving on cannabis versus alcohol, researchers stated that “Epidemiological studies have been inconclusive regarding whether cannabis use causes an increased risk of accidents; in contrast, unanimity exists that alcohol use increases crash risk.” 

They did mention that the effects of driving on both, alcohol and cannabis combined (cross-faded), were more enhanced than driving on either substance alone. And of course, alcohol and driving don’t mix, all studies will tell you that. But the fact remains, the results of their research were “inconclusive” as to whether cannabis was even that much of problem for drivers or not.  

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Another, more recent, study published in 2022 in the Journal of Studies on Alcohol and Drugs, claimed that legalization of recreational cannabis was associated with a 6.5% increase in injury crashes overall. However, the rates varied quite a bit, with some legal states reporting an 18% increase and others actually reporting up to 8% decreases in crashes. With such a wide range, it’s unlikely that cannabis has anything to do with the changes at all, and it’s likely something else (or a number of different factors) entirely. It’s also important to note that these statistics were only temporary. About 1 year post legalization, the numbers went back to normal.

Other studies even found that car accidents decreased overall in areas where cannabis was legal, and even more so near dispensary locations. In states/cities with dispensaries, insurance premiums went down by an average of $22 per year after legalization. According to the study authors, “we find premium reductions are larger in states with greater patient enrollment and in states that allow smoking.” They added that “existing legalization has reduced health expenditures related to auto accidents by almost $820 million per year with the potential for a further $350 million reduction if legalized nationally.”

Weed DUIs in the news 

With cannabis DUIs still being less charted territory from a legal standpoint, and because we know that weed doesn’t cause the same level of impairment as alcohol and other drugs, we rarely hear stories of arrests or car accidents related to cannabis use. However, some occasionally do make the headlines. The arrest of Pittsburgh Steelers running back Le’Veon Bell in 2014 for driving under the influence of marijuana got a lot of attention.