Last year, the National Highway Traffic Safety Administration released a report (pdf) called "Drug and Alcohol Crash Risk" that took a look at how often illegal drugs cause car accidents. In a finding that should surprise nobody, researchers found that people who used drugs were more likely to crash. "However," they added, "analyses incorporating adjustments for age, gender, ethnicity, and alcohol concentration level did not show a significant increase in levels of crash risk associated with the presence of drugs." In layman's terms, that means that you're not statistically more likely to get into a wreck if you're on drugs—but it's possible that if you're driving on drugs you'll also be drunk, or simply young and making bad decisions, which increases your chances of bending your vehicle around a telephone pole.
There may not be reliable statistics on the number of accidents caused by specific drugs, but thanks to years of studies we do know quite a bit about what certain chemicals do to your driving abilities. Here's a rundown of the worst things you can put into your body before you get behind the wheel.
Obvious disclaimer: Don't do drugs and drive. You're probably safest if you don't do drugs or drive, but definitely don't do both at the same time.
If you're a three-cups-a-day type of person, you'll probably protest that you need your morning coffee or you'll (at least figuratively) crash during your drive to work. Coffee has been shown to improve vigilance, and people have long assumed that stopping for caffeine can perk up tired drivers—but in 2011 researchers found that "improvements in driving performance and alertness after caffeine are likely to represent withdrawal reversal rather than a net beneficial effect of caffeine." In other words, you're better off just not drinking the stuff at all.
To make matters worse, if you're sleepy and you grab a cup of drive-thru coffee to wake you up, you're going to keep getting sleepy for an hour before the caffeine takes effect, meaning you might still be a danger on the road long after you think you're back in business.
More extreme sleep-killing drugs are even more hazardous for drivers. Cocaine may jolt you awake, but science says it also makes the world around you more frustratingly boring, leading coked-up drivers to engage in what the NHTSA calls "turning in front of other vehicles, high-risk behavior, inattentive driving, and poor impulse control," which is also known as "driving like an asshole." An Australian study found almost identical problems in meth-addled drivers.
MDMA, believe it or not, has a reputation for helping people's driving. The authors of a 2012 study noted, controversially, that the drug can "improve some psychomotor driving skills when administered during the day." But who takes ecstasy during the day? The meat of the study focused on people coming home after raves, and they tended to be pretty bad drivers in those conditions—but the researchers blamed the sleep deprivation, not the drug.
There's a good chance you've already driven after smoking pot, which I've already said is probably not a good idea.
But the major problem with driving while stoned is that increasingly, people are driving with both marijuana and alcohol coursing through their veins, as shown by an HBO documentary about the catastrophic 2009 Taconic State Parkway crash, which killed eight people and is believed to have been caused by a driver's lethal combination of marijuana and alcohol. "The two drugs potentiate each other, at which point one and one don't equal two anymore," Carol Weiss, an addiction psychiatrist at Weill Cornell Medical College, said in the documentary.
In that same film, Betsy Spratt, Director of Toxicology for Westchester County, said that "alcohol may increase the absorption of the marijuana," and that since pot "[is] a hallucinogen, your cognitive function can deteriorate pretty rapidly," resulting in drivers getting confused, lost, or, as in the case of the 2009 tragedy, driving the wrong way on a freeway for almost two miles before causing a deadly three-car pileup.
Opiates, meanwhile, can cause horrible, life-ruining addictions and fatal overdoses, but there are worse drugs to be on while behind the wheel. When it comes to pills like Vicodin and Oxycontin, a 2013 survey found that high doses were dangerous for drivers, but low doses weren't necessarily a huge problem. And having trace amounts of drugs hanging around in your bloodstream is a necessary part of day-to-day existence for methadone users in recovery.
Some stuff you can get at your corner pharmacy without anyone looking at you sideways can seriously impair your driving. Over-the-counter cough syrup with dextromethorphan (DXM), for instance, is notorious for being abused by suburban high schoolers. If they get behind the wheel of a car, they're probably no safer than drunk drivers. An Erowid user who enjoys the drug advises people, "Don't think for a moment that you can drive on DXM; even if you can't tell, it greatly reduces reaction time."
Meanwhile, Benadryl, according to Dr. John D. Weller of the University of Iowa, "may have an even greater impact on the complex task of operating an automobile than does alcohol." It produces such a heavy-duty high that the NHTSA commissioned a paper on it that detailed exciting effects like ataxia (lack of muscle coordination), tremors, hallucinations, and convulsions. That paper concluded the drug "clearly impairs driving performance." An Erowid user says a high dose of Benadryl caused a freakout behind the wheel that included hallucinations spanning "from shaky trees to just thinking trash cans were people."
No, Seriously, These Will Kill You
Then there are drugs with such pronounced effects you would think no one would actually take them and then try to drive, but then again, humans have a seemingly limitless capacity for stupidity.
Driving on LSD has obvious problems as well—who wants to be operating a huge machine in the middle of a trip?—but people still do it on occasion. Sometimes these stories can be almost cute, like when George Harrison and his wife drove around London really slowly in a Mini Cooper. But you are not George Harrison, in so many ways, and it's best if you avoid that sort of thing. Most people seem to know this already, which is why the NHTSA report on LSD says "the incidence of LSD in driving under the influence cases is extremely rare."
Just stay home, people. How hard is that?
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