Does Weed Kill Brain Cells? And 5 Other Things to Know
We don’t know for sure if using marijuana can kill your brain cells.
More research is also needed to determine whether each form of use — including smoking, vaping, and ingesting edibles — has a different effect on your brain’s overall health.
Studies evaluating the cognitive effects of long-term marijuana use are ongoing.
Here’s what we currently know about how weed affects the brain.
A well-known 2012 study from New Zealand evaluated marijuana use and cognitive ability in more than 1,000 individuals over a 38-year period.
The researchers reported an association between ongoing marijuana use and cognitive decline.
In particular, they found that:
- People who started using marijuana heavily as adolescents and continued as adults lost an average of six to eight IQ points by the time they reached midlife.
- Among the group above, people who stopped using marijuana as adults didn’t regain lost IQ points.
- People who started using marijuana heavily as adults didn’t experience any IQ loss.
This study had a significant impact for a few reasons.
First, it was among the first large, longitudinal (long-term) studies to assess marijuana use and cognitive functioning.
Next, the results suggest that marijuana use during adolescence may have an irreversible effect on adolescent brain development. Some additional research supports this conclusion.
However, the New Zealand study also has significant limitations.
For one, it isn’t possible to conclude that marijuana use causes lower intelligence based on this study alone.
While the researchers controlled for differences in participant education levels, they didn’t rule out additional factors that may have contributed to cognitive decline.
A 2013 reply to the New Zealand study suggests that personality factors may play a role in both marijuana use and cognitive decline.
The author cited conscientiousness as an example. Low conscientiousness might explain both drug use and poor performance on tests of cognition.
Genetic factors may also contribute to cognitive decline, as suggested by a longitudinal twin study from 2016.
In this case, the researchers compared changes in IQ between twins who used marijuana and their abstinent siblings. They didn’t find any significant differences in IQ decline between the two groups.
The key takeaway? More research needs to be done to understand how marijuana use affects intelligence over time.
Researchers haven't determined whether smoking weed kills brain cells, but that hasn't stopped some groups from comparing the substance to nicotine and alcohol, two established brain cell killers. Here's what the science actually says about marijuana's effects on the brain, which users are most at risk, and more.
How much brain cells does weed kill
“I’ll pretend I’m Jamaican, man,” said Jim Breuer, the fairly Caucasian and very-not-Jamaican character in the iconic weed comedy Half Baked.
“You have smoked yourself retarded,” replied his buddy, Thurgood Jenkins (played by Dave Chappelle), with a grimace.
Ableist slurs aside, Chapelle’s line illustrates a persistent and much-too-prevalent myth in our society: that smoking weed makes us stupid. Or, as some folks spin it, weed kills brain cells.
Is it true? No. If that was the case, most of you reading this would probably be drooling vegetables by now.
The human-vegetable example may not work on relatives, supervisors, or college professors who view your intellect with gross disdain simply because you puff on occasion (or all day, every day).
Thankfully, we got some real, solid science you can cite next time your marriage to mary jane is called into question by some strait-laced square.
History Time: The Bogus Rhesus Monkey Experiment
Back in the day, haters didn’t think tokers were necessarily unintelligent. But from the late 1800s to the 1930s, weed smokers were instead considered insane or psychotic by the Western (read: imperialist) medical community.
The brain-damage thing gained traction in the ’70s after President Richard Nixon – determined to crush the herb-loving, anti-war Black Power Movement and its white hippie allies – rigged federal research to show, with ‘scientific evidence,’ that smoking weed kills brain cells.
To do this, the Nixon administration convinced psychiatrist Robert G. Heath to conduct the infamous rhesus monkey experiment. In the so-called study, Heath took a bunch of monkeys, strapped gas masks to their faces, then pumped so much marijuana smoke into the masks that asphyxiation and carbon monoxide poisoning caused the monkeys’ brain cells to die.
At the time, only the study’s results were released to the public.
How Heath manipulated the experiment to please President Tricky Dick was kept secret until 1980, when Playboy and NORML got a hold of the full rhesus monkey study report. (By the way, no self-respecting scientist ever keeps their experimental methods a secret.)
Nixon’s shiny new National Institute of Drug Abuse (NIDA) spent years using Heath’s fabricated study to promote the idea that smoking weed killed brain cells, a myth that hit its zenith in the 1980s during Nancy Reagan’s ridiculous “Just Say No” anti-drug campaign.
Today, we should just say no to the silly notion that weed kills brain cells. For starters, there are way too many hyper-intelligent people who’ve admitted to regularly smoking cannabis.
Examples: if weed killed brain cells, then how did astronomer Carl Sagan receive the Public Welfare Medal in 1994, the National Academy of Sciences’ version of the Oscar? Or how did author Maya Angelou win a Pulitzer, a Tony, and three Grammys in her lifetime? And how did Snoop Dogg come up with all those velvety smooth rhymes?
What the Science Really Says
In 2016, Duke University conducted one of the many studies showing that cannabis use doesn’t harm the brain. The researchers followed identical twins — who are essentially genetic clones of each other — for 10 years. Among each twin pairing, one smoked weed and the other never touched the stuff. No differences were found between their neurocognitive functioning, even after one twin spent a decade blazin’.
But the Duke study only looked at outward, observable behaviors between the twins. How does a toker’s actual brain look compared to a non-toker’s?
In 2015, scientists at the University of Colorado-Boulder used high resolution MRI scans to compare the brain volumes, shapes, and structures of weed smokers and non-smokers. Guess what the researchers found? No differences between the brains. Zilch. Nada. Pot-laden brains looked just like the straight-edge ones.
So what can we draw from these two studies? Weed doesn’t appear to kill brain cells, but it also doesn’t make anyone smarter, either.
But What About All Those IQ Studies?
The prohibitionists’ favorite ‘stupid-pothead’ argument is that cannabis use lowers IQ scores. But first, a word on IQ, otherwise known as the “intelligence quotient.”
IQ only measures a specific kind of intelligence, namely, one’s ability to detect and exploit patterns within the narrow scope of word games and 3D mind puzzles. IQ can reasonably predict an individual’s success in certain fields, like science, business, or computers, but that’s pretty much it.
Over the years, psychologists and neuroscientists have determined there are several types of intelligence: star athletes demonstrate kinesthetic intelligence, artists exhibit aesthetic intelligence, musicians play off their own kind of smarts, and so on and so forth. Today’s IQ tests are useless for predicting anything in these other important disciplines.
Furthermore, the inventor of the IQ test, French psychologist Alfred Binet, never intended his test to serve as a measuring stick for someone’s higher intellectual capacities. He used it as a tool to help him diagnose mental dysfunction in his child patients.
Here’s what Binet had to say about his own test: “The scale, properly speaking, does not permit the measure of the intelligence, because intellectual qualities are not superposable, and therefore cannot be measured as linear surfaces are measured.”
In other words, human intelligence can’t be reduced to a single number because it’s too complex.
Anyway, you came here for scientific ammo. In 2018, researchers at the University of Arizona looked at 1,989 twins in England and Wales. Like the Duke University study above, they found no IQ differences between the twins when one smoked weed and the other didn’t.
Commenting on the Arizona study, drug researcher Ian Hamilton at York University told the Daily Mail that low-IQ teens are more likely to smoke weed because it stimulates their minds, which may explain why some psychologists notice lower IQ scores with tokers.
Regardless, the science certainly says smoking weed will screw with our short-term memories, as anyone who’s hit a bowl and then spent an hour looking for their car keys (which was in their hand the entire time) can attest to. But that’s about it.
Does it really matter if you can remember LeBron James’ NBA stats from the 2003-2004 season? No, it doesn’t, especially when weed can help any culdesac baller become a better player.
Just remember to consume responsibly, and your body — and your brain — will thank you for it later.
Next time someone tells you that you’re destroying your brain by smoking weed, just send them this scientifically-supported rebuttal of the anti-cannabis claim.