Study shows marijuana's long-term effects on the brain


The effects of chronic marijuana use on the brain may depend on age of first use and duration of use, according to researchers at the Center for BrainHealth at The University of Texas at Dallas.

In a paper published today in Proceedings of the National Academy of Sciences (PNAS), researchers for the first time comprehensively describe existing abnormalities in brain function and structure of long-term users with multiple magnetic resonance imaging (MRI) techniques. Findings show chronic marijuana users have smaller brain volume in the orbitofrontal cortex (OFC), a part of the brain commonly associated with addiction, but also increased brain connectivity.

"We have seen a steady increase in the incidence of marijuana use since 2007," said Dr. Francesca Filbey, Director of the Cognitive Neuroscience Research in Addictive Disorders at the Center for BrainHealth and Associate Professor in the School of Behavioral and Brain Sciences at The University of Texas at Dallas. "However, research on its long-term effects remains scarce despite the changes in legislation surrounding marijuana and the continuing conversation surrounding this relevant public health topic."

The research team studied 48 adult marijuana users and 62 gender- and age-matched non-users, accounting for potential biases such as gender, age and ethnicity. The authors also controlled for tobacco and alcohol use. On average, the marijuana users who participated in the study consumed the drug three times per day. Cognitive tests show that chronic marijuana users had lower IQ compared to age-and gender-matched controls but the differences do not seem to be related to the brain abnormalities as no direct correlation can be drawn between IQ deficits and OFC volume decrease.

"What's unique about this work is that it combines three different MRI techniques to evaluate different brain characteristics," said Dr. Sina Aslan, founder and president of Advance MRI, LLC and adjunct assistant professor at The University of Texas at Dallas. "The results suggest increases in connectivity, both structural and functional that may be compensating for losses. Eventually, however, the structural connectivity or 'wiring' of the brain starts degrading with prolonged marijuana use."

Tests reveal that earlier onset of regular marijuana use induces greater structural and functional connectivity. Greatest increases in connectivity appear as an individual begins using marijuana. Findings show severity of use is directly correlated to greater connectivity.

Although increased structural wiring declines after six to eight years of continued chronic use, marijuana users continue to display more intense connectivity than healthy non-users, which may explain why chronic, long-term users "seem to be doing just fine" despite smaller OFC brain volumes, Filbey explained.

"To date, existing studies on the long-term effects of marijuana on brain structures have been largely inconclusive due to limitations in methodologies," said Dr. Filbey. "While our study does not conclusively address whether any or all of the changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age of onset and duration of use."

The study offers a preliminary indication that gray matter in the OFC may be more vulnerable than white matter to the effects of delta-9-tetrahydrocannabinol (THC), the main psychoactive ingredient in the cannabis plant. According to the authors, the study provides evidence that chronic marijuana use initiates a complex process that allows neurons to adapt and compensate for smaller gray matter volume, but further studies are needed to determine whether these changes revert back to normal with discontinued marijuana use, whether similar effects are present in occasional marijuana users versus chronic users and whether these effects are indeed a direct result of marijuana use or a predisposing factor.

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More information: Long-term effects of marijuana use on the brain, PNAS,
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Nov 10, 2014

?? hunh...

Anyway the tldr; was that initial use increase certain connectivity in the brain, but continued severe usage degraded brain functionality. This is unnoticed in the individual and others as the increased connectivity may - not proven enhance IQ on a different level that offsets the brain impairment. So like almost all chemicals that can be put into the body, small amounts can be good, and going overboard for a long period of time is permanently bad.


This seems consistent with what most people who have observed intelligent people who smoke the drug. They are very functional people, however over a long period of time they seem to loose their edge faster than others.

Nov 10, 2014
It actually doesn't find any IQ differences and still is uncertain what this generally means, if anything important. This study mentions other similar studies have found confounding factors and inconsistent data ranging from increased brain size regions in pot smokers to virtually no differences. This study attempted to shore up those statistical parallax and more or less failed to explain if these changes are actually bad or just neuroadaptive features. Research noted that pot smoker's brains in this study observed enlarged _other_ regions while measurable decrease in grey matter and Orbitofrontal gryus with increases in other regions perhaps compensating/displacement for this observed 'decrease' is rather a shifting around of neural resources than some net decrease (pun intended), like someone who actually loses half their brain in a car accident is still functioning and somewhat normal in some cases -- how? The theory is neurons/axons aren't localized but redundant and distributed.

Nov 10, 2014
These results, I believe, are consistent with past CDC reports. It really is kind of obvious. If you use mind altering drugs, you alter your brain function. Sooner or later, the brain rewires to accept the new norm.

Nov 10, 2014
Whatever the results, 100 people isn't really a big enough sample. Did they control for genetic predisposition to early dementia? Or that people who smoke often become more philosophical and less fact driven? (good or bad, up to you) Or that, simultaneously, smart media use is changing the type of brains we have to be less factual memory oriented, and better at finding things we want to know about when we need to know about it? Plus a whole basket of correlation is not equal to causation. "While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use..." = NO DIRECT LINK. Perhaps people with already low volumes of gray matter are more likely to enjoy smoking because they have enlarged pleasure centers or less impulse control?

Nov 10, 2014
Somebody better tell the president. He famously smoked a lot of weed as a kid. And somebody should inform the patent office that they screwed up, too. They famously awarded the government a patent for the good that cannabis does for the brain.

Nov 11, 2014
This is just another dose of Reefer Madness. From the actual abstract of this study:

>>>"To date, however, findings remain inconclusive... longitudinal studies are needed to determine causality of these effects."

The similarities to the study discussed at Policy Mic in April are uncanny.

>>>"Chances are you saw the headlines on Wednesday: "Casual marijuana use linked to brain changes," "Marijuana re-shapes brains of users, study claims" or "Casual marijuana use may damage your brain." Oh my god, marijuana is bad for my brain!

"I think I saw one headline that was 'Marijuana reshapes the brain' and I groaned — that's not what we did," said Dr. Jodi Gilman, 31, author of the now-famous Harvard Medical School/Massachusetts General Hospital study on marijuana's effects, in an interview with PolicyMic.

"We never say marijuana causes these changes," Gilman said. The media may have given that impression in headlines, but the study doesn't show causation."

Nov 11, 2014
Marijuana doesn't harm the brain, or any other part of the body. In fact, research shows marijuana prevents the deadly swelling of brain trauma, gives the brain more stamina, helps prevent Alzheimer's and similar brain disease, and actually stimulates the production of new brain cells.

Nov 11, 2014
I personally don't think Texas can be unbiased in anything that is against their mores.

Nov 11, 2014
I can't help but remember the movies we saw in Drivers Education classes where they cut open the brain of an alcoholic and there are all those rotten holes. I think if MJ is simply shrinking your brain a bit then it is far better than alcohol yet one is illegal and one is legal. Hmm..

Nov 15, 2014
Smoking three times per day?!?!?! That seems really on the extreme side - or am I deluding myself?

Nov 15, 2014
It's very challenging to engage in chronic user marijuana studies over long time frames to establish the overall effects on the smokers' brains and IQ's. Chronic users are more likely to engage in alcohol use and abuse, which is known to seriously harm all of the body's organs, including the brain, and this will taint the results. They should be taken with a grain of salt. The article vacillates - it's harmful and it's not harmful etc.

I used to smoke pot for the heck of it when I was younger, but now I have a serious case of sciatica. It provides the best pain management with fewer damaging effects than long term ibuprofen (may cause spontaneous fatal ulceration of the digestive tract) or acetaminophen (liver damage in the long run) .

My IQ since high school (45 yrs ago) has jumped by 6 points (!), because I was a cabbie for a few years, and that occupation is known to increase IQ levels, so I conclude that pot use is not detrimental to intelligence.

Nov 16, 2014
I'd live to see this same scrutiny for tobacco and alcohol use. Sane laws based on real evidence would be a nice change - if it means treating previously assumed benign substances differently, so be it.

Nov 17, 2014
Hasn't had a negative effect on the information age. Have any ever worked or been around programmers?

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