Heavy marijuana use shrinks brain parts - study

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Heavy marijuana use shrinks brain parts - study

By Will Dunham

WASHINGTON, June 2 (Reuters) - Long-term heavy use of marijuana may cause two important brain structures to shrink, Australian researchers said on Monday.

Brain scans showed the hippocampus and amygdala were smaller in men who were heavy marijuana users compared to nonusers, the researchers said. The men had smoked at least five marijuana cigarettes daily for on average 20 years.

The hippocampus regulates memory and emotion, while the amygdala plays a critical role in fear and aggression.

The study, published in the American Medical Association's journal Archives of General Psychiatry, also found the heavy cannabis users earned lower scores than the nonusers in a verbal learning task -- trying to recall a list of 15 words.

The marijuana users were more likely to exhibit mild signs of psychotic disorders, but not enough to be formally diagnosed with any such disorder, the researchers said.

"These findings challenge the widespread perception of cannabis as having limited or no harmful effects on (the) brain and behavior," said Murat Yucel of ORYGEN Research Centre and the University of Melbourne, who led the study.

"Like with most things, some people will experience greater problems associated with cannabis use than others," Yucel said in an e-mail. "Our findings suggest that everyone is vulnerable to potential changes in the brain, some memory problems and psychiatric symptoms if they use heavily enough and for long enough."

Among the 15 heavy marijuana users in the study, the hippocampus volume was 12 percent less and the amygdala volume was 7 percent less than in 16 men who were not marijuana users, the researchers said.

The researchers acknowledged that the study did not prove it was the marijuana and not some other factor that triggered these brain differences. But Yucel said the findings certainly suggested marijuana was the cause.

"STONED" FOR 20 YEARS

While about half of the marijuana users reported experiencing some form of paranoia and social withdrawal, only one of the nonusers reported such symptoms, Yucel said.

The heavy marijuana users, average age 40, said they had used other illicit drugs less than 10 times, the researchers said.

A U.S. group supporting legal sales and regulation of marijuana took issue with the findings, particularly because they were based on men who were such heavy, long-term users.

"These were people who were essentially stoned all day every day for 20 years," Marijuana Policy Project spokesman Bruce Mirken said by e-mail. "This study says nothing about moderate or occasional users, who are the vast majority -- and the (study) even acknowledges this."

"The documented damage caused by comparably heavy use of alcohol or tobacco is just off-the-charts more serious, and you don't need high-tech scans to find it," Mirken added.

Yucel said the researchers have begun new research on the effects of both short-term and long-term and moderate and heavy use of marijuana. (Editing by Maggie Fox)

http://www.reuters.com/article/latestCrisis/idUSN02271474
 
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News just in!

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"But marijuana makes people forgetful!"
 
I wonder, by what action did they determine this?

It just doesn't seem logical that because of short term memory not being used (if your stoned 24/7; the prerequisite set by the study) would actually cause parts of your brain to shrink or be totally inactive.

What are the results of testing in non-users for comparison? Over what amount of time was the study conducted?

Not sure what to make of it all.

Guess it goes to show, moderation is key.
 
These dudes smoked everyday for 20 years... and in that time used other drugs a max of 10 times. I don't want to insinuate using hard drugs is "cool", but I'd rather be an opiate/amphetamine addict than some burn out who smokes pot all day every day till their 40's and 50's. The thought of it just scares me.
 
15 samples and 16 controls! The sample size of this study is laughable, if it applied to anything other than marijuana then the scientific community would laugh it out of existance and it would have not have gotten any press coverage.

I do not look twice at a study unless the sample size is in the triple digits or more.

Also they were smoking 5 joints a day for 20 years, wonder what the toll would be if it was converted into alcohol consumption. (liver failure, serosis of the liver, stomach ulcers, heart disease and irreversible brain damage.)
 
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CloudyHazeD said:
I wonder, by what action did they determine this?

It just doesn't seem logical that because of short term memory not being used (if your stoned 24/7; the prerequisite set by the study) would actually cause parts of your brain to shrink or be totally inactive.

What are the results of testing in non-users for comparison? Over what amount of time was the study conducted?

Not sure what to make of it all.

Guess it goes to show, moderation is key.
i also question the science of the study

they either had marijuana in their system at the time, or temporarily quit for the study which would mean some sort of rebound effect would be going on

both of those would effect the results
 
toastedpanda said:
These dudes smoked everyday for 20 years... and in that time used other drugs a max of 10 times. I don't want to insinuate using hard drugs is "cool", but I'd rather be an opiate/amphetamine addict than some burn out who smokes pot all day every day till their 40's and 50's. The thought of it just scares me.


really? you love those withdrawals and cavings and pawning electronics huh?
 
why does everyone think pot just simply could not possibly affect people's brains on a long term basis? I mean is it that proposterous to believe that if someone had 5 joints a day for 20 yrs there may be less than desirable effects on the person's brain? Quite plausible but as others said sample size not great but it is just a start in what I beleive will be more firm evidence in this area.

5 joints a day is nothing for a hardcore daily smoker either. In my 7-8yrs of smoking pot I would have easily doubled or tripled the amount they have had so I guess my hippocampus and amygdala are rooted.

But on a side note the basis of the study was a reduction in volume of the hippocampus and amygdala. Is a reduction in volume of a sector of the brain a hard and fast proof of the persons inadequacy in that sector? Like how about they became overactive and efficient and hence their volume shrunk to adjust and to regain equilibrium :)
 
Kaneh Bosm said:
15 samples and 16 controls! The sample size of this study is laughable, if it applied to anything other than marijuana then the scientific community would laugh it out of existance and it would have not have gotten any press coverage.

really? i work at a major research university and we do studies on things other than marijuana with sample sizes as small as n = 5. the results certainly aren't laughed out of existance. rather, they are often used to decide whether to pursue further research into the subject.
I do not look twice at a study unless the sample size is in the triple digits or more.

well, that's your problem. studies can certainly be useful with sample sizes less than triple digits. it all depends on what you are studying and what conclusions you are attempting to draw and how strong a case you want to make for them.
 
burn out said:
.... it all depends on what you are studying and what conclusions you are attempting to draw and how strong a case you want to make for them.

yeah.

so, he's right.

15 Ps is a crap sample by anyones standards, except for a prelim or a case-by-case analysis.


this data is being presented as "generalisable",
headliner conclusions and implications are being drawn,
when, in fact, the sample is crap.
 
The_Idler said:
yeah.

so, he's right.

15 Ps is a crap sample by anyones standards, except for a prelim or a case-by-case analysis.


this data is being presented as "generalisable",
headliner conclusions and implications are being drawn,
when, in fact, the sample is crap.

only the media headline is doing that. the article says Long-term heavy use of marijuana may cause two important brain structures to shrink, Australian researchers said on Monday...The researchers acknowledged that the study did not prove it was the marijuana and not some other factor that triggered these brain differences.
 
burn out said:
only the media headline is doing that. the article says Long-term heavy use of marijuana may cause two important brain structures to shrink, Australian researchers said on Monday...The researchers acknowledged that the study did not prove it was the marijuana and not some other factor that triggered these brain differences.

which makes the study crap.

because the sample was miniscule.

because if you have only correlational relationship,
you need a very large sample to support it.

o.O
 
burn out said:
really? i work at a major research university and we do studies on things other than marijuana with sample sizes as small as n = 5. the results certainly aren't laughed out of existance. rather, they are often used to decide whether to pursue further research into the subject.


well, that's your problem. studies can certainly be useful with sample sizes less than triple digits. it all depends on what you are studying and what conclusions you are attempting to draw and how strong a case you want to make for them.

In humans where thousands of variables can change the outcome of the study then a sample size needs to be at least a three digit figure, I have a background in Stats. too. What were you studying that a single digit sample size could satisfy the needs of the study? The effectiveness of a brand of vaccum cleaner?
 
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