A New Study Just Explored The Difference Between Driving Drunk vs. Stoned

March 25th 2015

As lawmakers nationwide explore the benefits of legalized marijuana, there are common questions being raised: how will tax structures apply? How will it be regulated? Who can use it, and how can we make it safe?

One expansive area covered by broad safety conventions is the road––don’t drive inebriated. In this arena, marijuana, it would seem, fits under the larger umbrella of mind-altering substances categorically outlawed for drivers. But according to a new study, lawmakers may have to take a second look at the drug.

Last month, researchers from the National Highway Traffic Safety Administration (NHTSA) reported that drivers who use marijuana are significantly less likely to crash than drunk drivers. That much may seem obvious, but here’s the kicker: drivers with THC in their systems (adjusted for age, gender, race, and alcohol use) were no more likely to crash than those who had not used drugs or alcohol before getting behind the wheel.

The study more or less confirmed what we largely already knew: alcohol is a terrible mixer with driving. Going against conventional logic, though, marijuana (as well as other drugs like antidepressants, painkillers, and stimulants), was found to cause no statistical change in the risk of a crash for a driver who had used the given substance prior to driving. Alcohol, however, increased the risk by nearly seven times for a blood alcohol concentration of 0.05 and above. 

Could smoking while driving be safer than drinking?

The key takeaway, then, is that the influence of pot (and other drugs mentioned above) on the mind and body is harder to define than the effects of alcohol while driving. “Most psychoactive drugs are chemically complex molecules, whose absorption, action, and elimination from the body are difficult to predict,” the report notes, “and considerable differences exist between individuals with regard to the rates with which these processes occur. Alcohol, in comparison, is more predictable.”

Despite the numbers, this is not to say it’s necessarily safe to drive stoned. One pitfall of the NHTSA study is that THC can be detected in the body days or even weeks after the actual pot is consumed. So essentially, the study contains no good measure of how safe it is to drive a car directly after a few bong rips compared with a day or two removed from said rips. The NHTSA admits as much: “At the current time, specific drug concentration levels cannot be reliably equated with a specific degree of driver impairment.” By the same token, though, this shortcoming highlights the need for more research, especially given that states with legalized pot are already running into problems crafting driving regulations.

In Colorado, lawmakers have tried to set limits for blood THC content to determine what constitutes “marijuana-impaired driving.” But unlike similar limits for alcohol content, Colorado’s threshold of 5 nanograms per milliliter strikes some as far too low for frequent users of marijuana. A reporter for Westword took this theory to task, discovering that after a night of sleep and 15 hours without smoking, his THC content was nearly triple the legal threshold. “I and thousands of other medical marijuana patients may be risking arrest every time we drive,” he wrote, “even when deemed sober by a doctor[.]” Similar thresholds are in place in Washington.

As marijuana use rises in states with fully legalized pot, it’s important to keep in mind that driving while impaired by any substance, including marijuana, is dangerous. But the study illustrates that current legal limits are perhaps ineffective measures, and that more research is needed on the subject. And while we wait for more comprehensive, scientific examination of the subject, amateurish local TV station experiments will have to do.

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