Imagine a time when it wasn’t accepted that drunk driving made you more likely to get in an accident, when there wasn’t consensus about what constitutes drunk driving, nary a clue about how to measure your impairment, and no idea about whether anti-drunk driving laws were necessary or how they should work. All of this happened with alcohol, and it’s happening again with cannabis.
Cannabis is legal to some extent in a majority of states, and while it is generally accepted that cannabis use overall has grown in the past 10 years, there is no evidence that marijuana use in states where it has been legalized has contributed to more fatal car crashes than in states where it is illegal.
So, is it OK to drive if I’m high? I mean, it’s legal, right?
Nope. Alcohol is legal, but drunk driving isn’t. Codeine and oxycodone are legal, too, if prescribed by your doctor, but it’s illegal to drive under their influence. Similarly, it is illegal, even in places where cannabis is legal for recreational use, and yes, even if you have been okayed to use it for medical reasons, to drive while you’re impaired by marijuana. Period.
How Do I Know if I’m Impaired? Or Is it OK to Drive If I’m Just a Little High?
Define “a little high.” (Anti-drunk driving activists might similarly ask you to define “buzzed” or “a little drunk”.) The problem is that nobody really knows what “impairment” means when it comes to cannabis. You might have seen charts that tell you, based on your sex and weight, how many alcoholic drinks consumed over how many hours are likely to qualify you as impaired or intoxicated.
But alcohol is unique. It is relatively simple to track the way that it is absorbed, distributed, and eliminated from the body (its pharmacokinetics) and how those processes affect your brain and body (its pharmacodynamics) but these processes are far more complex and variable for drugs, including cannabis; at this point we don’t know enough to make up a similar chart for weed. The presence of THC—the primary psychoactive component in cannabis—in the driver’s body has not been shown to be a reliable measure of driver impairment.
Peer-reviewed research suggests that cannabis users wait a minimum of three to four hours after use before driving; NORML, a non-profit that works to legalize cannabis, suggests that users not drive while they feel impaired which, yes, includes feeling “a little high” or “buzzed.”
How Does Cannabis Impact Driving Skills?
Does consuming cannabis impair your driving ability? Contribute to car crashes? Dunno. Though it’s generally agreed upon that you shouldn’t drive if you feel even “a little high,” as mentioned above, the National Highway Transportation Safety Administration is struggling to find concrete answers to these more specific questions. Their July 2017 report to Congress on “marijuana-impaired driving” points out that currently, no one has figured out how to measure how stoned someone is just sitting on their couch, let alone developed a tool—akin to the breathalyzer—that can quickly and accurately be used roadside by law enforcement.
From driving simulation research we know that using cannabis has been shown to impair key driving-related skills including reaction time, tracking ability, and target detection; cognitive skills like judgment, anticipation, and divided attention; and executive functions like route planning and risk taking. But they didn’t find a clear link between cannabis use and car crashes.
We also know that whereas people under the influence of alcohol tend to underestimate how impaired they are, those under the influence of cannabis tend to overestimate it. Compared to a sober person, someone who has consumed cannabis typically drives more slowly, follows other cars at greater distances, and takes fewer risks. Those who have consumed alcohol do the opposite: they generally drive faster, follow at closer distances, and take greater risks. Some researchers—the NHTSA among them—say that cannabis users’ behavior suggests that they’re trying to compensate for how messed-up they feel. However, these researchers caution that a driver’s conscious attempts at conservative driving still can’t make up for the whole raft of skills that cannabis impacts. Advocates for cannabis legalization point to studies showing that drivers under the influence of cannabis are only slightly more likely to be involved in crashes than those who are sober, and are much less likely to get into accident than those who are impaired by alcohol (or alcohol combined with other drugs, including cannabis).
What Happens if You’re Pulled Over While You’re High?
With alcohol, if you are involved in a crash or pulled over by law enforcement for erratic driving you will be given a breathalyzer test. If this test reveals that your blood alcohol concentration (BAC) is over the .08 limit, you are considered, guilty of drunk driving.
Since there is no marker like BAC for cannabis, there’s also no breathalyzer-type gizmo with which to measure how much cannabis you’ve consumed. That said, there are other tests that law enforcement rely on to measure your impairment if you’re pulled over or involved in a crash. In addition to the Field Sobriety Test, you might be subjected to a Drug Influence Evaluation (DIE), in which a trained Drug Recognition Expert (DRE) looks for physiological manifestations of drug use including blood pressure, pupil size, and red eyes. Depending on where you live, you might not encounter a DRE; there are only some 8000 of them in the country—you can see a map of DREs by state here.
What’s the Deal with DUID (Driving Under the Influence of Drugs) Laws and Cannabis?
Five states (Montana, Nevada, Ohio, Pennsylvania, and Washington) have per se DUID laws which work the same way as alcohol per se laws: If a blood test shows that you have more than a specified amount of THC in your blood (generally 5 nanograms of THC per milliliter of blood), you don’t have to have failed the Field Sobriety Test or the DIE to be found guilty of DUID. (Colorado law also imposes a 5ng/ml THC in blood threshold but this threshold is not per se; a defendant may successfully argue that they were unimpaired despite having more than 5ng/ml THC in their system.)
There are also now “zero tolerance” per se laws in 11 states (Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Oklahoma, Rhode Island, Utah, and Wisconsin) which take things one step further: in these states, anyone found with any measurable level of THC or its one of its metabolites (a substance necessary for its metabolism) in their blood will be convicted of DUID. Yes, even though blood draws are not done roadside and even though THC can linger in the blood for up to 30 days and its concentration in blood has not been proved to correlate with impairment.
But in most states, the DUID laws are “effect based.” In order to convict you, a prosecutor must prove that your observed impairment and/or incapacity at the time of a crash or traffic stop was due to the ingestion of cannabis rather than just how much THC was in your blood when you were tested. To prove their case, prosecutors typically rely on all of the evidence at their disposal: results of the Field Sobriety Test, testimony from a Drug Recognition Expert, plus toxicological exam results indicating recent consumption of a controlled substance.
DUI laws vary by state but nowhere is it legal to drive if you’re impaired and nowhere, under any circumstance, is it advisable to do so. Inside every steel-reinforced car or truck are the soft bodies of our friends, neighbors, and family members so proceed with caution.