Dazed and Confused

06.12.14

The Truth About Driving While Stoned

Recent stories about a ‘new’ study showing marijuana DUIs have tripled are recycling an old study that proved nothing of the sort. It’s high time we separate fact from fiction in the stoned-driving debate.

Nathan Palmer was headed to his job at a Peoria, Illinois, Pizza Hut in July 2011 when his car crossed the median and struck a motorcycle, instantly killing its driver. Despite the smell of marijuana, the 33-year-old told police he hadn’t smoked in a week, and that the crash was the result of “losing consciousness.”

In Illinois, which houses some of the tougher DUI laws in the nation, even smoking a joint a week before can implicate you. Authorities found trace amounts of THC (the psychoactive chemical in marijuana)—enough to send Palmer to prison. But after months in court, the judge dropped charges against Palmer, citing evidence that hypoglycemia—low blood sugar—was the likely cause.

The story captures the disorder that still pervades the stoned-driving debate today. Without a “weed breathalyzer” or any tool to measure recent marijuana use, the line between anecdote and fact has been indelibly blurred. Had hypoglycemia not been a factor, Palmer's case would have come down to whether or not the THC in his system was impairing him at the time. A loaded question with no easy answer.

It’s an issue further complicated this week by a piece in USA Today which details a “new” study that allegedly proves marijuana DUIs tripled nationwide in one year. The concept is not only inaccurate, it’s recycled—similar to an article titled Pot Fuels Surge in Drugged Driving Tests, published by NBC in January. The report claims not only that the study measured for cannabis and risk of accident, but that it was a sampling of national data.

It was neither.

The study’s authors never intended to imply that marijuana caused the accidents, nor suggest that their sample was nationally representative. Analyzing the toxicology reports from 24,000 driving fatalities in six states during 2010, the authors found that 12 percent of those killed had marijuana in their system—triple what the number was in 1999.

But the study didn’t analyze whether marijuana caused the fatal accidents—only that it was present at the time of death. Since THC is fat soluble, it stays in the system much longer than alcohol. The Centers for Disease control estimates that, in some users, it can be detected up to two weeks after use. It is impossible to know whether the 12 percent with marijuana in their system smoked an hour or 14 days before their fatal crash.

Marijuana may have contributed to many of these accidents—perhaps all of them. But the study’s authors are disbelieving of that notion. “The prevalence of non-alcohol drugs reported in this study should be interpreted as an indicator of drug use, not necessarily a measurement of drug impairment,” the authors write. One of the study's authors, Guohua Li, elaborated on the point in a February story in the Denver Post. “The most likely explanation [for the rise] is that use of marijuana in the general driver population has been increasing, which may reflect increased use in the overall population,” Li said.

The truth is, after decades of analysis, we still don’t have a firm grasp on how THC impairs driving.

Laboratory studies have confirmed that THC (officially, Delta-9-tetrahydrocannabinol) impairs many motor skills necessary for driving. But actual driving simulation studies have not mimicked these results. One sound example is a 2004 study in which three researchers found THC to inhibit attention, reaction time, hand-eye coordination, short-term memory, time and distance perception, and concentration.

But when tested in actual driving simulation, the authors found the results did not “replicate” their laboratory evidence. In other words, researchers were able to prove that THC should, technically, impair driving, but not that it does. Their explanation for the discrepancy: Drivers with THC are likely cognizant of their impairment and are thus able to “compensate...by driving more slowly and avoiding risky driving maneuvers.”

Dr. Paul Armentano, the deputy director of NORML (a nonprofit lobbying organization for marijuana reform) who has written extensively in peer-reviewed literature on the subject of cannabinoids’ influence on psychomotor performance, calls reports on the paper “highly” misleading. “[This] paper itself sought to draw no conclusions in regard to whether cannabis was a likely cause of accident or whether crashes in which cannabis played a causal role are increasing,” Armentano tells The Daily Beast. “It simply measured cannabis prevalence.”

He further suggests that applying this study to the nation as a whole is irresponsible: “[The authors] reviewed data from six states only—four of which were Hawaii, New Hampshire, West Virginia, and Rhode Island—hardly the states one would assess if you were doing a random sampling of the country.”

Kevin Sabet, executive director of SAM (Smart Approaches to Marijuana), says the study does hold importance. “This is further evidence...that marijuana is harmful for driving. It is directly related to car crashes,” he tells The Daily Beast. “I think it's reflective of the growing acceptance of marijuana and the growing ignorance about its harms, especially for drivers. Many teens today think driving while stoned is safe.”

In Sabet's eyes, it’s anything but safe. “Science has determined that cannabis intoxication doubles your risk of a car crash. Despite this scientifically valid fact, people are not getting this message,” he says. One commonly referenced example, a 2012 paper from the British Medical Journal, looked at close to 3,000 studies on the topic. Their analysis found drivers who had consumed cannabis twice as likely to be involved in a traffic accident.

The National Institute on Drug Abuse (NIDA) echoed Sabet’s sentiments in a paper released this week about the risks associated with marijuana and driving. In relation to the study, the agency told The Daily Beast: "The bottom line is that we are seeing broader use of more potent cannabis, thus we can expect more serious outcomes."

But NIDA's claim that marijuana use increases the likelihood of an accident is contradicted in some of the government’s own research. One, a U.S. Department of Transportation study from 2000, measured the effects of a low dose of THC with and without alcohol on driving proficiency of recreational users of marijuana and alcohol. The results showed that while THC and alcohol combined impaired driving, THC had only a negligible effect on driving. “Low doses of marijuana (THC 100 μg/kg) taken alone, did not impair city driving performance and did not diminish visual search frequency for traffic at intersections in this study,” the study reads.

Another, published in 2012 by the Journal of Accident Analysis and Prevention, found that the odds ratio for the likelihood of a marijuana positive driver being culpable in a traffic accident compared to a drug-negative driver to be on par with penicillin and antihistamines.

Mark Kleiman, a drug policy expert and professor at UCLA, says driving stoned is hazardous, but much less hazardous than driving drunk. Marijuana, according to a 2013 Columbia University case-control study, holds a relative risk of 1.83—meaning that driving 10 miles stoned is equally dangerous to driving 18 sober. This number falls significantly below those of other factors. In the same study, alcohol is shown to have a relative risk of 12; alcohol combined with something else, 23. According to data from the National Safety Council, the relative risk of texting is 4. “You shouldn’t be driving stoned," says Kleiman. “But there are many things that will degrade driving just as much if not more—having a 4-year-old in your back seat, sleepiness, texting.”

Beyond the relative risk associated with marijuana, Kleiman says blood is not a good proxy for how stoned you are. “It’s almost impossible not to be guilty of driving while stoned if you smoke. The fact that THC is fat soluble and then comes back out in your bloodstream means you can be THC positive when you’re not impaired at all,” he says. “There’s no way to tell if you’re breaking the law—that seems unjust.” Kleiman says THC mouth swabs are being tested that could present a viable solution to the drugged-driving debate.

In the meantime, the two states where recreational marijuana is already legal are ignoring the buzz and focusing on keeping the streets safe.

“Marijuana has been around for a long time,” Colorado State Trooper Nate Reid tells The Daily Beast. “State troopers across the country have been stopping people for marijuana for a long time. Now that it’s legal recreationally you still aren’t allowed to drive on it." According to data from the Colorado State Patrol, 374 out of the 2,314 DUIs statewide already this year—12 percent—have been due to marijuana.

But without data from years past to compare it to Reid is hesitant to claim this as an increase: “It's too soon,” he says.

A noble attempt to change the landscape of the marijuana DUI debate—where fiction often precedes fact.