Driving While Stoned: Is It an Issue?

By: Alexis Cantor & Christopher Pauli

Driving under the influence: when have you had too much?

With alcohol, you can check.

On Amazon, for the price of a meal, you can buy an alcohol breathalyzer. Responsible drivers have the option to do just that. So after a miracle Vikings victory celebrated with shots, their blood alcohol level is a reliable indicator of whether they’re likely to plow their Prius into a pole.

For Cannabis, there is no such thing yet and although Cannabix Technologies is developing a cannabis breathalyzer, it seems to be geared towards law enforcement use and not towards the everyday person.

So an occasional smoker is left to wonder:

Is smoking and driving as dangerous as drinking and driving?

How do I measure the dangers of smoking?

Does my tolerance affect my ability to drive high?

Unfortunately, science has yet to clear up these questions, and here at the Agricultural Genomics Foundation (AGF), we trust science.  

Over the past ten years, numerous research groups have studied the effects of cannabinoids when driving; however, the conclusions drawn from those studies warrant further investigation.  With Cannabis being second to alcohol in impaired driving accidents, understanding its effects is essential, especially in light of increased legalization.

Despite studies in the past showing increased impairment after Cannabis use, there is some disagreement about the role that  tolerance plays in the impairment of the user.  A study of 18 men and seven women showed that impairment changed between  groups that reported frequent use (more than four times a week) and groups that showed infrequent use (less than two times per week). In other words, they found that smokers with a tolerance were less impaired in their tests than smokers without a tolerance. However, another study that focused on tolerance and impairment studied 122 participants using both Cocaine and Cannabis. They found there was no significant difference in certain measures of impairment between the infrequent users (more than two times in the past three months) and daily users when given the same amount of Cannabis. Although most measures of impairment were independent of tolerance in their study, they did find that subjective intoxication and psychomotor performance correlated with the frequency of use. This means that users perceive themselves as less intoxicated even when impaired.

A few other real world tests have indicated that tolerance matters. Take the fascinating reports from TV stations in Washington State and Britain, which, while not scientific, are informative (and hilarious). With real drivers driving real cars while really stoned, Cannabis did impair their driving. But it did so at wildly different levels depending on tolerance. They show that potheads can — no surprise — drive better stoned than marijuana-naive subjects.

Ultimately, they’ve learned one valuable piece of information: Stoned drivers drive slow. Really slow.

And the more they consumed, the more slowpoke they became. In one test for the BBC, the correspondent couldn’t force herself to get the car up to a speed that was high enough to perform the test. In contrast, when drunk she continuously drove above the recommended speed.  

Also, when she was stoned she felt nervous. Drunk, she felt confident. The suggestion is: booze makes you think you’re in control, even though you’re reckless. Weed is the opposite: you think you’re driving like a menace, even if you’re driving like a granny.

Despite numerous studies done on the intoxicating effects of Cannabis, it is difficult to determine the actual effect. When testing for the presence of Cannabinoids, researchers are looking at THC, 11-OH-THC, and THCCOOH, which can lead to some misleading data collection. This is largely due to the discrepancies in how long Cannabis continues to affect an individual. THC and THCCOOH can be  detected up to 30 days after use, while  11-OH-THC can be detected 15 days after using Cannabis. When considering many accidents involving drivers with metabolites of Cannabis, it may not be fully accurate to label these drivers as under the influence of Cannabis at the time of the accident. Thus, one group decided to form a Cannabis Influence Factor to decide what level of metabolites would better suggest when someone’s under the influence. The results were mixed.

Although the science isn’t fully there to describe how to test when someone’s impaired, police forces have already begun using roadside tests for Cannabis Impairment. Colorado has decided to set an arbitrary limit of Cannabinoids in the blood at 5 nanograms per milliliter of blood, but this isn’t as clear as the legal limit of alcohol. While it’s known by most that one standard drink will leave you under the legal limit of 0.05 in Colorado, smoking a joint from a dispensary isn’t quite the same. A study from 1995 at Johns Hopkins University found that four puffs of Cannabis with 1.75 percent THC correlates to 57 ng/ml, while ten puffs can increase that to as much as 99 ng/ml. . The National Highway Traffic Safety Administration published in their July 2017 report that 90 percent of THC levels in the blood are dissipated within the first 30 minutes after smoking; however, with an average of 150 ng/ml, it is shown that a heavy-using driver would not be under the 5 ng/ml for hours or days after using Cannabis. So there could be lots of people ticketed for piloting high when, in fact, they’re clear headed.         

It’s safe to assume that for at least a couple hours after smoking even a couple puffs of Cannabis that is 20 percent or more THC, you would be well above the legal limit to drive. It’s always better to be safe than sorry when it comes to driving under the influence and use Lyft or Uber to get around after smoking. Numerous studies demonstrated impairment from Cannabis; however,  determining if this impairment is dangerous on the road should be the focus of future research.

AGF  is essential in providing the public with solid information regarding both the Cannabis industry and science. As AGF researchers, we aim to analyze and interpret research from around the world and share it with the public. Ultimately, the type of foundational information AGF provides will help in understanding the diversity of the Cannabis species.

Edited by Reilly Capps (@ReillyCapps)