Does Marijuana Change Young Brains?

(Photo: Brett Levin)

(Photo: Brett Levin)

Our latest podcast compared the costs of marijuana use to the costs of alcohol use.  A new study in the current issue of The Journal of Neuroscience argues that casual use of marijuana affects the developing brain.  Jason Koebler, writing for Vice, summarizes the findings:

High-resolution MRI scans of the brains of adults between the ages of 18-25 who reported smoking weed at least once a week were structurally different than a control group: They showed greater grey matter density in the left amygdala, an area of the brain associated with addiction and showed alterations in the hypothalamus and subcallosal cortex. The study also notes that marijuana use “may be associated with a disruption of neural organization.” The more weed a person reported smoking, the more altered their brain appeared, according to the Northwestern University and Harvard Medical School study, which was published in the Journal of Neuroscience.

The finding already has the study’s authors calling for states to reconsider legalizing the drugHans Breiter, the lead author, said he’s “developed a severe worry about whether we should be allowing anybody under age 30 to use pot unless they have a terminal illness and need it for pain.

(HT: The Daily Dish)

Nick Wood

So any problems with the study? I'm no neuroscientist, but there seems to be a certain amount of subjectivity here on the part of the participants and in the researcher's conclusions. I also think I hear familiar frames that have been used to keep it illegal... like the suggestion that marijuana use is linked to schizophrenia. This one is particularly frustrating to anyone who works with people with psychiatric disabilities because it not only keeps people going to jail for minor marijuana related offenses, but it gives society the impression that people with schizophrenia who need help have really simply brought it upon themselves and therefore deserve our indifference. Hogwash. I expect Freakonomics and VICE to give this one a more critical eye.


Yes, but which comes first - does the weed cause the difference in brain structure, or do those with a different brain structure smoke more weed?

They might have covered it in the study, but I can't find an open version of the original study.


So all those people saying marijuana is a gateway drug really were on to something.


It's important to be extra careful when scrutinizing politically-loaded subjects, such as anything having to do with marijuana.

I want to know how closely the "control group" matched the test group for all characteristics except use of marijuana, for example.

Also, there's a lot of variance between someone who takes a puff on a one-hitter on a Saturday afternoon before doing housework, and a pothead who gets high twice a day or more--yet both would count as people who smoke weed "at least once a week."

Finally, one of the most dangerous ideas around marijuana right now is the notion that it should be considered medicine only. When 99% of pot smokers are using the stuff recreationally, what is needed is honesty and clarity in reasoning for its legalization: "It's fun to get high, and not as dangerous as it's made out to be. Let adults use the drug for pleasure in a responsible, private way and make them pay for the consequences if they abuse the privilege, just like we do with alcohol."

Pushing for the legalization of marijuana as-medicine-only is disingenuous and will only cloud the issue in a stinky green fog of bad faith, deceit, and false "lab-coat legitimacy".



This study does not find anything of the sort. Correlation does not equal causation, especially not with a sample size of 20 individuals.

Lior Pachter, a computational biologist, calls it "quite possibly the worst paper I've read all year "

Brian W

So are these changes in the brain actually harmful? It looks to me that the researchers just found that there were changes, and didn't actually go the next step and figure out a) did those changes have an impact? and b) is it a negative impact?

Chris Mikaitis

From the study:

" Participants in this study were 20 young adult (age 18–25
years) current marijuana users and 20 controls. Marijuana and control
participants were matched on age, sex (9 males and 11 females in each
group), handedness, race, and years of education. All participants were

Clearly they have covered all their bases. I don't need any more evidence... come on, they're all right handed. How much clearer can it be?

Rick Bhasin

I love it when all these potheads try to argue against the validity of a science study showing that weed makes one stupid and apathetic. First have the patience to get a decent grade in statistics and organic chemistry before giving us your retarded oppinions. Even then you are merely a pion. It takes a decade of graduate level study of complex interdisciplinary subjects to truly understand the merits of a scientific study. I dont need a study to show me potheads are idiots. I have grown up with extremely smart people who have ruined thier brains and lives because of this drug. Yes there are some smart people who smoke pot, but those individuals could have been even smarter if they didn't smoke it. If you think this drug does not affect your intelligence and life in general it's only because your willing to settle for less because of your addiction. But each to their own. I am actually for the legalization of all drugs. The way I see it, the more idiots spending their time getting high and dumb, the less competition for me in life and business.



"Even then you are merely a pion."

Are you saying I'm some sort of lightweight meson? I think them's fighting words...

Oh, and I did get decent grades in statistics and organic chemistry, not to mention math, physics, and yes, even spelling :-)


So James, you seem to take offense to Rick's "high and mighty" comments. We can now assume that you smoke pot... :)


Humm... Change in brain. That's called learning, no?

For a reality check (if one is still needed after reading the Lior Pachta link above), go to Google Scholar and search on "exercise changes brain". Or chess, music, meditation, driving a cab in London... I suspect just about any reasonable choice will find plenty of hits.


Stupidity and apathy are not exclusive to cannabis users. I am a biochem major and a successful chef whose restaurant just won #1 in the world for our chosen specialty. My closest friend is a rocket scientist for NASA and has sent rockets to other planets. We smoked when we were younger, and still do (although not as much). It's not the cannabis sir, it's the person. Not all who smoke are lazy, and not using does not make for a hardworking genius.


If you look at the group called "weekly pot smokers" you'll see that most of them are indeed idiots. However, this is because most people *in general* are idiots, and the most idiotic of these idiots are further encouraged, by our laws and our culture, to smoke pot.

Thus, Rick Bhasin's complaint about potheads may be valid overall, even though he is wrong about the specifics.


Doesn't everything change a young brain? Wouldn't you be able to repeat this, but with kids that start playing soccer and find changes? If they like it wouldn't it show changes in the left amygdala?

I don't think pot is for kids, but I'm not sure this study is able to make the correlations it is trying to.


Steve Jobs did pot & LSD and I wouldn't dare to have called either dumb, lazy, under-performer or otherwise ...

But I truly think he had a brain that had developed traits that differentiated him from most other people in his generation (in both extremes) but I wouldn't depict that as an illness but rather a trait commonly found in genius ...

I'm not in no way trying to imply that there was causality between the use of drugs and genius although it seem to be common trait in geniuses thru history.



"They showed greater grey matter density in the left amygdala, an area of the brain associated with addiction and showed alterations in the hypothalamus and subcallosal cortex. The study also notes that marijuana use “may be associated with a disruption of neural organization.”

I might be wrong but haven't researchers found that people who suffer from schizophrenia, deep depression and PTSD suffer from smaller and less dense left amygdalas? And the shape of your brain changes with different genres of books you read.


I've developed a severe worry about whether we should be allowing doctors to limit the choices of grown f--king adults.

Show me external costs which outweigh potential tax revenue.


There are so many good arguments for legalizing pot, why shoot yourself in the foot with that unpersuasive silliness about potential tax revenue?


Correlation is not causation. Do these people have the developed "addition node" because they smoke marijuana once a week or do they smoke weed once a week because they have a more developed addition node?