"Heavy Marijuana use shrinks brain parts"

Forbosis.

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Rueters said:
By Will Dunham

WASHINGTON (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.

Original Link
http://www.reuters.com/article/lifestyleMolt/idUSN0227147420080602?pageNumber=2&virtualBrandChannel=0
 
I hate it how studies like this are reported, and yet no mention of 'problems' with the research is mentioned. Such as the fact that cross sectional study designs do not prove causation. Definitely in the area of mental illness were these things premorbid conditions? Also 15 heavy users is a pretty damn small sample size.
Not saying that their findings don't mean anything, just that newspapers regularly report these things results improperly.
 
How exactly do they determine brain size if the people are still alive?

Were the marijuana users physically the same size as the non-users, or were they hand picked for their small physical stature and smaller overall body size?

Societal withdraw due to drug use...
I dunno about that.
I have a STRONG pull for being social with those that stand against society - as they view it as an oppressive force.

I'm not social with people who worship the state and ignore science and reason when it comes to public policy.

Is that societal withdraw, or just disillusionment of the idea of the "State" that is beyond question?
I dunno...

At least the bit of the brain that shrunk makes these people with "brain damage" from their drug use less likely to get upset and aggressive when told they have problems because of their drug use.
They're also less afraid of further harm - so they'll probably keep using anyway ;)
 
Here comes the inevitable "this can't be true" posts. Seperate studies have confirmed that marijuana use reduces the activity of the hippocampus up to 50%, so by the action of activity induced neuroplasticity alone you would probably see a decrease in the size of that particular structure. I am not saying marijuana is the devil drug, but Jesus people it is not a completely benign psychoactive plant. The more drug users deny any of the real issues with the drug the more they will be discredited just like the rabid reefer madness fanatics.
 
Haha this is a terrible study. 15 subjects in a cross-sectional study! Are you kidding?!
 
You know, I don't need a study that measures brain size to tell you that weed makes people stupid. I stopped smoking because I couldn't function on the shit. I might get flamed for this, but of course weed effects the memory! Of course it effects learning! Why? Not because our brains shrink, fuck that's stupid. It's because we don't give enough of a shit to learn new stuff.

Enlitx said:
so by the action of activity induced neuroplasticity alone you would probably see a decrease in the size of that particular structure.

That's exactly what popped into my head. And like another poster said, without an autopsy how would they know the size of the hippocampus in our brains?

Scientists are smarter than this. It's the reporters that must be doing it.
 
This is complete BS!!!! Sounds like the shit they would say in highschool health class..... the teacher actually told us that smoking Marijuana would make young men grow female breasts... fuck that and fuck the people who did conducted this so called "study"
 
At first I was kind of worried this article might have a shred of validity but then I read this....
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.
That pretty much says everything right there. Only 15 subjects and a marginal difference between the two groups. This is not science.
 
Care said:
At first I was kind of worried this article might have a shred of validity but then I read this....

That pretty much says everything right there. Only 15 subjects and a marginal difference between the two groups. This is not science.

What sample size would you like to see, what difference between the groups would not be marginal?

7% and 15% seem pretty decent differences to me.
 
They never said the results were statistically significant or anything, but I wouldn't be surprised if marijuana does affect the brain - especially in the hippocampus and amygdala. It makes sense that these two areas would be affected.
 
The results were statistically significant.

Context: Cannabis is the most widely used illicit drug in the developed world. Despite this, there is a paucity of research examining its long-term effect on the human brain.

Objective: To determine whether long-term heavy cannabis use is associated with gross anatomical abnormalities in 2 cannabinoid receptor–rich regions of the brain, the hippocampus and the amygdala.

Design: Cross-sectional design using high-resolution (3-T) structural magnetic resonance imaging.

Setting: Participants were recruited from the general community and underwent imaging at a hospital research facility.

Participants: Fifteen carefully selected long-term (>10 years) and heavy (>5 joints daily) cannabis-using men (mean age, 39.8 years; mean duration of regular use, 19.7 years) with no history of polydrug abuse or neurologic/mental disorder and 16 matched nonusing control subjects (mean age, 36.4 years).

Main Outcome Measures: Volumetric measures of the hippocampus and the amygdala combined with measures of cannabis use. Subthreshold psychotic symptoms and verbal learning ability were also measured.

Results: Cannabis users had bilaterally reduced hippocampal and amygdala volumes (P = .001), with a relatively (and significantly [P = .02]) greater magnitude of reduction in the former (12.0% vs 7.1% ). Left hemisphere hippocampal volume was inversely associated with cumulative exposure to cannabis during the previous 10 years (P = .01 ) and subthreshold positive psychotic symptoms (P < .001). Positive symptom scores were also associated with cumulative exposure to cannabis (P = .048 ). Although cannabis users performed significantly worse than controls on verbal learning (P < .001), this did not correlate with regional brain volumes in either group.

Conclusions: These results provide new evidence of exposure-related structural abnormalities in the hippocampus and amygdala in long-term heavy cannabis users and corroborate similar findings in the animal literature. These findings indicate that heavy daily cannabis use across protracted periods exerts harmful effects on brain tissue and mental health.

It's really starting to piss me off that people complain about sample sizes etc when they see any research with which they disagree. You need a sufficiently large sample size to have sufficient power to measure the effect size you expect to see, that's all, otherwise you're just throwing your grant money away.

Ok so it doesn't prove that there are not pre-existing differences or other confounding factors, and prospective studies would be better, but it doesn't mean you should rubbish it just because it doesn't fit your agenda.
 
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Ernestrome said:
What sample size would you like to see, what difference between the groups would not be marginal?

7% and 15% seem pretty decent differences to me.
Almost all scientific studies that test the effect of certain variables on humans use a much larger sample size, at least 10x this one. There are too many other variables that could affect the findings. 15 people is not going to give an accurate representation of the population because its too easy to skew the results one way or the other.

As far as the difference between the hippocampus and the amygdala sizes go its very hard to determine what is actually a "normal" size. How do we know that their control group had a "normal" brain size? If the sample size was bigger with the same results I would have to admit that its a pretty significant difference, but its not.

I would bet this study gets ripped apart if it ever gets peer reviewed.
 
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Ernestrome said:
but it doesn't mean you should rubbish it just because it doesn't fit your agenda.

uhhh....yeah...you should. if you're gonna do science, you gotta do it right. plus the research is from australia. they are more on reefer madness than the UK. i wanna see a more controlled studys with more subjects that aren't heavy but normal smokers if they are gonna claim anything. i'm not saying i doubt MJ as having different effects on the brain but these claims are far fetched for having only 15 subjects and them being heavy users(smoking 5 joints a day). :p
 
Yeah, If the sample size was more along the lines of 75+ subjects (35+ in each group), and not "recruited from the general community", I'd take these results more seriously.
 
Where would you like them recruited from?

Hasn't it been peer reviewed if it got into archives of general psych?
 
I think if you do the math, you will find these results statistically significant, and 15 a reasonable sample size. But does that rule out tampering with the sample (hand picking, for example), to fit an agenda? No.
 
There are several things that could be done betterdifferently/better.
Match controls and users.
Have former user and light current user groups too.
Maybe bigger groups.

Also archives gen psych has the highest impact factor of the psychiatry journals (IF=15.98 ), so it's not some backwater dumping ground for crap studies, but it's not nature (IF= 53) either :)

Nonetheless, i don't think you can discard the results of this study because it could be improved upon, it's not meant to be definitive, it's just a signpost on the way.
 
I believe insignifigant results such as these should not be published anywhere. they should just be used as an outline to start more in-depth studies. once they test further then those results should be published. stating that this test is what led them to go more in depth looking at the amygdyla and hippocampus
 
Stickreid said:
I believe insignifigant results such as these should not be published anywhere. they should just be used as an outline to start more in-depth studies. once they test further then those results should be published. stating that this test is what led them to go more in depth looking at the amygdyla and hippocampus

But the results were significant :!

Clearly not getting the incremental progression inherent in science are we...
 
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