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.

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.

There is evidence, though, that for older people, THC helps prevent against the brain inflammation that leads to Alzheimer’s disease.

Nietzsche said that when marrying, you should ask yourself, “Do you believe that you will be able to converse well with this person into your old age?” But perhaps the better question is, “Will this person’s geriatric fingers be able to roll a really excellent doob?”

Will legalizing pot make people drink less?

Rick Wilking/Reuters

Possibly! There are some signs that pot and alcohol are substitutes, at least for teens: A 2013 study from professors at Montana State University and the University of Colorado at Denver found that marijuana legalization “was associated with reductions in heavy drinking, especially among 18- through 29-year-olds. In addition, they found that legalization was associated with an almost 5 percent decrease in beer sales, the alcoholic beverage of choice among young adults.” Another study found that marijuana legalization led to a 13 percent decrease in fatalities involving alcohol.

The same author found that legalizing marijuana does not increase its use among teens, but other studies have shown that marijuana use among young people drops off significantly once they reach 21, suggesting that young people are only smoking until they can legally imbibe booze.

Is smoking pot as bad for your lungs as cigarettes?

“We don't know. Nobody's done that study,” said NIH director Francis Collins when he was asked the question at a recent dinner with journalists.

A longitudinal study published in JAMA (a really good journal!) found that marijuana does not impair lung function in normal users. But a study that tracked weed-smoking Swedes over 40 years found that the heaviest users had double the risk of contracting lung cancer.

“The literature seems to indicate that if you're a heavy user of marijuana, that may be associated with an elevated risk of cancer of the lung. But it has to be very heavy use,” Nora Volkow, director of the National Institute on Drug Abuse, told National Geographic. “For milder use, the risk seems to be much lower. There is some evidence of a heightened risk of testicular cancer, though, which is a fairly rare form of cancer.”

Is it addictive?

About 10 to 14 percent of people who smoke pot may get strong urges to keep doing it, but for most, the drug is not really habit-forming—or at least it’s less so than alcohol, caffeine, and other narcotics are. One 1999 study published in the journal Psychopharmacology found that people who had smoked pot at least 5,000 times (the equivalent of daily for 14 years) had slightly elevated aggressive behavior levels three to seven days after they stopped smoking. But their behavior returned to normal after a month had passed.

A 2004 study found that people “withdrawing” from marijuana experienced muscle pain, chills, decreased food intake, and decreased self-reported sleep quantity. At the same time, though, marijuana makes some people eat more, sleep more, and experience euphoria, so it could be that these folks were simply returning to a typical, lackluster homosapien existence.

And another paper found that people look forward to smoking and feel emotionally tied to the idea of smoking ... but everything from yoga to boba tea has been described as similarly “addictive” by its avid fans.

“Marijuana is different from a lot of other drugs of abuse in that although there usually are some subtle physiological signs of withdrawal when a chronic user stops smoking—mildly elevated pulse, irritability, and so on,” wrote Wes Boyd, a Harvard psychiatrist, at Psychology Today, “these physical effects are generally fairly mild, and they are dramatically less obvious or powerful than those seen when a habitual user of alcohol, opiates (either heroin or any of the opioid pain pills), or benzodiazepines (such as Xanax or Klonopin) abruptly ceases use.”


So, to toke or not to toke? Some people take the medical ambiguity surrounding pot as a sign that smoking is rather safe. Others see it as a reason to avoid the drug until we have better data.

Considering that we just found out that even eating too much protein can cause early death, though, it might be wise to proceed cautiously. Which is probably how you’re already proceeding, if you’re high.