You would not expect a federal agency to announce to everyone that it’s safe to drive while stoned out of your gourd, but that’s more or less what happened last week. The full paper is available online and is full of helpful charts and tables showing the relative risks of various drugs, both legal and illegal.
First things first: this study showed (for approximately the billionth time) that no one should ever drink and drive,
[blockquote type=”left, center, right”]Based on the adjusted risk [they adjusted for things like youth and gender], drivers with a BrAC [breath alcohol content, measured with a Breathalyzer] of 0.05 are approximately 2 times more likely to crash than drivers at zero BrAC. At 0.08 BrAC the adjusted relative risk of crashing is approximately four times that of drivers at zero BrAC. At a BrAC of 0.10 the adjusted risk increases to approximately 6 times, and at 0.15 BrAC drivers are at least 12 times as likely to crash.[/blockquote]
It’s worth noting that even at a blood alcohol level of 0.03, your risk of crashing goes up 20%. If you’re a 150 pound woman and have a single drink, that’s your likely blood alcohol level right there. Legal? Yep. Safe? Well, it’s legal.
And right there, we’re already into the weeds on this study. They measured drunkenness with a Breathalyzer. They measured pot use with a saliva test. Saliva tests are gaining in popularity because they’re less invasive than a blood test, less gross than a pee test, and give much more current information than a hair test. It’s a particularly good test if you’re approaching strangers by the side of a highway and asking them to voluntarily participate in your study.
The problem with any marijuana test is that THC stays detectable in your system for a while. A saliva test is one of the better ones: it’ll usually stop detecting THC after a day or two. But it definitely can’t be relied on to show your impairment right now; a positive test just tells them that sometime in the last day or two, you used marijuana. If they’d also tracked drivers who sometime in the last day or two used alcohol and combined them with the drunks to see what sort of numbers they found, this would have given us a much more apples-to-apples comparison.
This gets increasingly complicated when you look at studies on chronic marijuana users — people who use the drug every day, either for medical reasons or because they really like getting high. In 2011 a Colorado pot advocate had his own blood drawn and analyzed fifteen hours after last smoking and was found to have a blood level of THC well over the cutoff for impairment under the current laws of Colorado, because the drug builds up in your tissues. That’s also why it can turn up on urine tests weeks after someone last smoked a joint. His statement that he was not impaired at all might have been more impressive if he’d provided us with some benchmarks and maybe a test of his reaction times. But in fact, studies suggest that chronic users get used to the effects enough to pass field sobriety tests even immediately after consuming marijuana. Which is not entirely surprising. There are a long list of legal drugs, both prescription and over-the-counter, that can impair driving, including basically anything that lists “drowsiness” as a potential side effect. The usual advice is to avoid driving until you know how a drug affects you, not to swear off driving forever.
Past studies have found that if you get participants high, they exhibit an impaired reaction time and have trouble completing tasks that require multitasking. They also do exactly what any sensible person would do if they realized that their reaction time was impaired: they slow way down. One of the reasons why driving drunk appears to be such an incredibly bad idea is that drinking impairs judgment along with everything else, and drunk drivers tend to have a grossly inflated estimation of how competently they’re driving.
A 2013 study examined people who’ve been in crashes, and found that your chances of being at fault in a crash doubles if you’ve smoked marijuana but also notes that the risks are much higher for occasional users. They focused on blood tests, precisely because they were trying to exclude the people who might have used pot sometime this week in favor of the people who are high right now. I’ll note, though, that the risk level they found (doubled!) is the same as the people driving around with a 0.05 blood alcohol level, which is below the legal limit in every state.
So – maybe we shouldn’t be worried about the stoned people on the road? Unless we’re in a hurry, and they’re in front of us on a one-lane road? My personal take-away from this study is that we should not use the specter of stoned drivers as an argument against legalizing pot: they are not a major concern. However, anyone who’s sitting down to smoke a recreational bowl should plan to smoke at home or take a taxi: it absolutely does impair you. It just probably won’t still be impairing you tomorrow.
[Photo via Shutterstock]