What Is Your Brain on Pot?

As more states legalize, we still don’t have a clear picture of how marijuana affects the body.
Jason Redmond/Reuters

On February 27, a memo might have gone out to all the research assistants, speechwriters, and publicists in Maryland: “Folks: Google for the fact you want, then Google the source it came from.”

That’s the day Annapolis Police Chief Michael Pristoop cited—apparently inadvertently—the fake news site The Daily Currant in his testimony against marijuana decriminalization in the state.

“The first day of legalization, that’s when Colorado experienced 37 deaths that day from overdose on marijuana,” Pristoop said, according to the Capital Gazette. “I remember the first day it was decriminalized there were 37 deaths.”

Pew Research Center

Unfortunately, Sen. Jamie Raskin, a Democrat who had proposed the legalization bill, was in the room and had used the Internet recently.

“Unless you have some other source for this, I’m afraid I’ve got to spoil the party here,” Raskin said in response. “Your assertion ... was a hoax on the Daily Currant and the Comedy Central website.”

Chief Pristoop, in certain circles, that’s what’s known as “harshing one’s mellow.”

Of course, no one has ever died from smoking pot.

... Or so it was thought, until a study in the U.K. last month found that two recent deaths could not be attributed to anything other than “cannabis intoxication.”

Obviously, those men might have had underlying conditions the researchers weren’t aware of. But as legalization and decriminalization sweep the nation, the British study speaks to a major problem with marijuana research: Nearly every question about the drug’s safety, its long-term effects, and its impairment potential is up for debate.

Medical marijuana is already legal in 20 states and the District of Columbia, and about 14 states are considering passing similar laws this year. At least a dozen states are considering decriminalizing the drug. D.C. voted this week to drop the fine for possessing up to an ounce of weed to just $25, less than most parking tickets.

But as pot becomes mainstream, the uncertainty over its health impacts prompts head-scratching statements like Pristoop's, scaremongering about addiction, and cranky editorials that advocate abstaining from pot in favor of “higher pleasures”—which I’m pretty sure is the name of a sativa strain.

One big reason we don’t have better pot research is that the drug is still illegal at the federal level, so researchers have a hard time getting their hands on grant money. The government’s only foray into bud so far has been the National Institute on Drug Abuse, which operates a tiny federal marijuana farm at the University of Mississippi. And if a pot study did get under way, prospective subjects would be worried that by signing up they’d be admitting to drug use (or admitting to being interested in drug use) and exposing themselves to arrest.

With that in mind, here is a rundown of the best guesses we currently have as to what marijuana does to the body. Fortunately, the answer is probably not “kills you on the first day it’s legal.”

Does pot impair drivers more than alcohol does?

First of all, don’t drive under the influence of anything! Spend your substance-induced haze on the couch in your underwear watching Cake Boss like a respectable human being!

Okay, with that out of the way ... alcohol appears to be way worse.

Colorado Department of Transportation

A 2009 Yale University meta-analysis seems to be the clearinghouse on all things weed-and-wheels related: It says both pot and alcohol increased drivers’ reaction times and the number of incorrect responses to emergency situations. Stoned drivers were worse than sober drivers at tasks like staying in a straight line (a.k.a.: a lane), didn’t monitor the speedometer as well, and had worse reaction times in passing, braking, and responding to a changing light. And pot combined with even a small amount of alcohol is a disastrous combination for driving.

But while stoned driving doubles your risk of a car accident, drunk driving at the legal limit of .08 BAC triples it. This could be because pot-smokers realize they’re stoned and try to compensate accordingly. Interestingly, the Yale study found that people who smoked a third of a joint thought they were impaired as drivers, but they were not actually all that impaired. Meanwhile, people who drank the equivalent of a small glass of wine thought they were fine but were actually pretty discombobulated.

How does marijuana affect memory?

It’s not good for your memory, at least if you start smoking as a teenager. In one study published in December, researchers examined teens who smoked marijuana daily for three years and found that the memory-related structures in their brains appeared to “shrink and collapse inward,” and that they performed worse on memory tasks. The troubling thing? This was two years after the subjects stopped smoking. And the younger the teens were when they started lighting up, the worse the impairment seemed to be.

University of Michigan Institute for Social Research, 2012 

An earlier study in rats found that THC, the active ingredient in pot, weakened the connections between neurons in the hippocampus, the brain structure critical for memory formation. But another study on human subjects found that the “skunk” strains of pot, which have a greater ratio of THC to cannabidiol, are worse for memory than hashish or herbal strains. And researchers who followed nearly 2,000 young Australian adults for eight years found that any differences in memory and intelligence between those who smoked pot and those who didn’t could also be attributed to gender or education, and the differences disappeared after the individuals stopped smoking.

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Olga Khazan is a staff writer at The Atlantic, where she covers health.

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