Heavy marijuana use may damage developing brain in teens, young adults

February 2, 2009
Yellow areas in the brain of a heavy marijuana smoker show brain regions with the most significant abnormalities. These areas correspond with those under development during normal adolescent years. Credit: The Children's Hospital of Philadelphia

Adolescents and young adults who are heavy users of marijuana are more likely than non-users to have disrupted brain development, according to a new study. Pediatric researchers found abnormalities in areas of the brain that interconnect brain regions involved in memory, attention, decision-making, language and executive functioning skills. The findings are of particular concern because adolescence is a crucial period for brain development and maturation.

The researchers caution that the study is preliminary and does not demonstrate that marijuana use causes the brain abnormalities. However, "Studies of normal brain development reveal critical areas of the brain that develop during late adolescence, and our study shows that heavy cannabis use is associated with damage in those brain regions," said study leader Manzar Ashtari, Ph.D., director of the Diffusion Image Analysis and Brain Morphometry Laboratory in the Radiology Department of The Children's Hospital of Philadelphia.

The study appeared early last month in the Journal of Psychiatric Research. The current research builds on previous work by Ashtari and colleagues, who used the same imaging technology to analyze normal brain development in adolescent subjects.

In the current study, working with child psychiatrist Sanjiv Kumra, M.D., now at the University of Minnesota, Ashtari and colleagues performed imaging studies on 14 young men from a residential drug treatment center in New York State, as well as 14 age-matched healthy controls. All the study subjects were males, with an average age of 19. The researchers performed the imaging studies at Long Island Jewish Medical Center.

The 14 subjects from the drug treatment center all had a history of heavy cannabis use during adolescence. On average, they had smoked marijuana from age 13 till age 18 or 19, and reported smoking nearly 6 marijuana joints daily in the final year before they stopped using the drug.

The study team performed a type of magnetic resonance imaging scan called diffusion tensor imaging (DTI) that measures water movement through brain tissues. "The abnormal patterns of water diffusion that we found among the young men with histories of marijuana use suggest damage or an arrest in development of the myelin sheath that surrounds brain cells," said Ashtari. Myelin provides a coating around brain cells similar to insulation covering an electrical wire. If myelin does not function properly, signaling within the brain may be slower.

Myelin gives its color to the white matter of the brain, and covers the nerve fibers that connect different brain regions. "Our results suggest that early-onset substance use may alter the development of white matter circuits, especially those connections among the frontal, parietal and temporal regions of the brain," said Ashtari. "Abnormal white matter development could slow information transfer in the brain and affect cognitive functions."

Ashtari added that the findings are preliminary. Among other limitations of the study, such as a small sample size, five of the 14 subjects with heavy cannabis use also had a history of alcohol abuse, which may have contributed an effect. Also, it is possible that the brain abnormalities may have predisposed the subjects to drug dependence, rather than drug usage causing the brain abnormalities.

"Further research should be done to investigate the relation between repeated marijuana use and white matter development," said Ashtari. "However, our work reinforces the idea that the adolescent brain may be especially vulnerable to risky behaviors such as substance abuse, because of crucial neural development that occurs during those years."

Source: Children's Hospital of Philadelphia

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3 / 5 (2) Feb 02, 2009
I know one case of somebody who smoked a lot of marijuana since he was 12 and today is faculty at Caltech in astrophysics. Poor guy, if did not smoke marijuana when he was a youngster, he probably would be a .... doctor?
not rated yet Feb 03, 2009
I know lots of people with professional jobs that have smoked cannabis for years (since 16 or 17).

I assume that they would have been geniuses had they not smoked.

Or, perhaps they would have been a lot dumber had they not smoked ?

Research needs to be done properly with proper goals and controls. Otherwise it is more than a waste of time.

Perhaps these researchers started smoking in infnacy ?

not rated yet Feb 03, 2009
Nobody wants to imagine their brain was affected in some way they can't now fix. So the reception for this news isn't going to be unbiased.

I know smart people who smoke. But I don't know very successful AND extremely smart people who smoke regularly. Not one.

Would Mauricio's Caltech acquaintance get further in his career if he didn't smoke? Probably. How would smoking help his career?
5 / 5 (1) Feb 06, 2009
So know that we know cannabis is harmful to children, this is all the more reason to LEGALIZE it. That way the government can regulate the age for purchasing it because a poll conducted on teens proved that it was easier for them to buy marijuana from a dealer than it is to purchase cigarettes from a gas station.

LETS STOP ALL THE IGNORANCE PEOPLE. Marijuana is one of the SAFEST substances known to man in its natural form and has caused, ZERO deaths, EVER. As in there have been no known records of ANYONE ever dying due directly to weed even after going back over 10,000 years. Lets compare to that to all the legal substances; including caffeine, alcohol, tobacco which have killed HUNDREDS OF THOUSANDS. Don't even get me started on how legalizing cannabis including hemp would completely turn our economy and provide millions of new jobs.
not rated yet Feb 25, 2009
Cannabinoids act on the endo cannibinoid system which is most abundant in the hippocampus between the temporal lobes. The area indicated is not the hippocampus......
not rated yet Aug 26, 2009
I seriously doubt legalizing cannabis would do much for the economy, other than maybe a few million in extra taxes. But I don't agree that this will reduce young teens from smoking cannabis.

The natural consequence of legalizing pot is that pot useage will increase and become a part of our cultural norms. I don't really see a down side to this, especially when we can refine the chemistry of cannabis and isolate the compounds that cause the most pleasant experiences and minimize the harmful effects we've seen like memory loss and psychosis.

What I think we can all agree on is the fascist-eugenics era "marihuana" laws in the USA are absurd, unconstitutional, and cause more social and economic destruction than this mild intoxicant ever did.

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