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Your Brain On Pot

We all remember Reefer Madness--the 1936 classic about the supposed evils of cannabis. Decades later, a lot of people think marijuana is pretty harmless. In fact, there's a whole movement touting the medicinal properties of the weed. But despite the long debate about the pros and cons of pot smoking, it remains far from clear how innocuous or dangerous it really is. Well, some new research might surprise a lot of people--especially the Woodstock Generation.

Murat Yucel at the University of Melbourne in Australia and his colleagues did brain scans on 15 men who were big-time pot heads, meaning they smoked at least five joints a day for more than a decade. The researchers compared them to 16 similar men who did not smoke pot.

The scans revealed some striking differences in the brains of the pot smokers, according to a paper in the June issue of the Archives of General Psychiatry. A part of their brains known as the hippocampus, which regulates emotion and memory, was about 12 percent smaller on average. Their amygdalas, which is involved in fear and aggression, was about 7 percent more minuscule.

When the researchers tested the subjects' thinking and emotions, they found the pot smokers had more trouble remembering words. In fact, even though they were only pushing 40 on average, their verbal memories were more like men in their 50s and 60s. And about half of the cannabis-users reported experiencing some form of paranoia and social withdrawal, compared to only one of the non-users. The more pot the subjects smoked the more likely they were to show these signs.

The study involved men who smoked a lot of pot, and the findings may not hold true for moderate or occasional users. And there's always the chicken-and-egg question of whether the pot smoking affected the mens' brains or people with those kinds of brains were more likely to smoke pot for some reason. But with an estimated 15 million Americans smoking pot each month, and perhaps 3.4 million using it daily for a year or more, the researchers say more study is clearly needed to answer these questions.

By Rob Stein  |  June 5, 2008; 7:00 AM ET
Categories:  Alcohol and Drugs  
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I agree that this needs a bigger study and more investigation! For one thing, there's significant anecdotal evidence that heavy pot smoking affects men and women differently, possibly due to hormonal changes that, for instance, causes heavy dope smoking males to develop breasts. There are so many problems with this "research" I'm not sure where to start...first and foremost: they studied only FIFTEEN men? It's likely that a number this low makes the "results" invalid. Then of course, there's the huge quantities these guys used--five joints a day for more than 10 years? I'm guessing that the number of people who smoke this much pot is very, very low--hey, maybe that's why they only studied 15 men! I'm amazed that the subjects were even able to get enrolled in a study and didn't get lost on the way. How did they remember how long and how much they've been smoking?

Posted by: Mildly amused | June 5, 2008 9:07 AM | Report abuse

Totally meaningless sample size. Hard to believe this comes from a "University".

Posted by: Sanuk | June 5, 2008 9:38 AM | Report abuse

More "Reefer Madness" indeed. This story got big play dpwn here, where attitudes toward marijuana are straight outta the 1950s. One thing I don't see from this so-called "study" is HOW MUCH ALCOHOL DID THESE GUYS DRINK? I'm a hospital nurse. I've dealt with hundreds of heavy drinkers over the years. I've seen them wig out violently due to delerium tremens, and suffer Wernecke's Syndrome when they're withdrawn from the sauce without B-vitamin supplements. I HAVE NEVER SEEN A SINGLE PERSON SUFFERING FROM BRAIN DAMAGE DUE TO MARIJUANA! This report is more Puritan propaganda.

Posted by: Bukko in Australia | June 5, 2008 10:21 AM | Report abuse

Five joints a day!

That is ALOT of smoking.....WAY more than an average daily smoker is going to ingest.

Larger sample size, lower the threshold of what they consider a subject who smokes alot...then let's see what the study says.

Posted by: Silver Spring | June 5, 2008 11:35 AM | Report abuse

Yeah...But was it good weed?

Posted by: willandjansdad | June 5, 2008 12:10 PM | Report abuse

Hmm, I'd be paranoid, too if I used that much pot and knew that if I got caught by the cops it wouldn't go well for me. :-D

Posted by: OldBAM | June 5, 2008 12:29 PM | Report abuse

I smoked alot in the 70's and I can't remember if it affected me or not

Posted by: OldBAMSsis | June 5, 2008 12:38 PM | Report abuse

I can't remember the 70's!

Posted by: Anonymous | June 5, 2008 12:48 PM | Report abuse

Smoking dope can affect one's emotions. Pot can exacerbate the problems of someone who already suffers from depression. Perhaps these problems may exist more for those who would already have problems (i.e., those predisposed to problems).

Incidentally, five j's a day is well within the boundaries of consumption.

Posted by: Tom | June 5, 2008 1:19 PM | Report abuse

31 test subjects?

"Relaxed" verbal memories?


I'd bet the study was done with a Hypothesis of "brain holes" and all they could come up with afterwards is that the test subjects were less able to memorize words and were more peaceble in nature.

Reefer Madness indeed. This is a joke.

Posted by: Ifyougotem | June 5, 2008 1:53 PM | Report abuse


That's the best they can do? Reduced memory and reduced areas of aggression?

Ooooohhhhh. Scary.

Oh and by the way, I challenge anyone to a game of memory, and 1 hour beforehand i'll smoke 5 joints and you drink five martinis.

Lets base a study on the outcome of that game. I bet my undersized hippocampus and amygdalas will kick your cirrhotic liver's butt anyday - and outlive you in the process.

Posted by: The Challenger | June 5, 2008 2:04 PM | Report abuse

The only "news" about this study is that it is headline news in a "respectable" paper like the Washington Post. Name a prescription drug for which the results of a 15-person study would generate world-wide headlines. Regardless of the underlying accuracy or methodology of this study, it is being used as yet another piece of propaganda.

I want to see some genuine and unbiased research on this subject, not this garbage masquerading as science. However, since our greedy pharmaceutical companies can't make a buck off a drug which is already in the public domain, don't hold your breath.

I bet that if you scanned the brains of 15 Washington Post reporters, you would find signs of serious degradation in mental performance over the past eight years...

Posted by: Steve | June 5, 2008 2:19 PM | Report abuse

RE: Tom's "five j's a day is well within the boundaries of consumption"

What are YOU smoking? I have smoked moderately for two decades, have a Ph.D. from an elite school, and have many pothead artsy friends... and have never met anyone who smokes nearly that much. Even one joint per person per day is a bit too much, unless that is ALL you are doing all day. Tom, looks like you are in the Puritan tradition of "Reefer Madness" morons.

Posted by: JG | June 5, 2008 2:26 PM | Report abuse

15 men who have smoked 5 or more joints a day for at least a decade? Of course, these 15 men never used any other drugs, including alcohol.

This "study" is a joke, and not even a good one.

Posted by: Pagun | June 5, 2008 4:14 PM | Report abuse

Could it be that people who smoke that much weed have reduced brain functions anyway? This study has identified correlation, not causation. The experimental group is not randomly selected, and surely suffers from self-selection bias.

The correlation identified may exist, but it's not necessarily pot that is damaging their brains.

I also agree with the other comments on sample size. 15 people is an awfully small sample to draw strong conclusions.

As a non-smoker, I don't think smoking (anything) is a terribly good idea -- but this seems like weak science to me.

Posted by: J | June 10, 2008 12:51 PM | Report abuse

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