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http://www.medicalnewstoday.com/articles/109397.php
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Structural abnormalities in the hippocampus and amygdala may be associated with long-term, heavy cannabis use, according to an article released June 2, 2008 in the Archives of General Psychiatry, one of the JAMA/Archives journals.
Cannabis is a classification of plants that has many human applications but is famously used in the production of marijuana, which is consumed for its psychoactive effects. The long-term effects of cannabis use have long been debated, according to the article: "Although growing literature suggests that long-term cannabis use is associated with a wide range of adverse health consequences, many people in the community, as well as cannabis users themselves, believe that cannabis is relatively harmless and should be legally available." The authors continue, quoting statistics regarding cannabis use in the United States: "With nearly 15 million Americans using cannabis in a given month, 3.4 million using cannabis daily for 12 months or more and 2.1 million commencing use every year, there is a clear need to conduct robust investigations that elucidate the long-term sequelae of long-term cannabis use."
To investigate the long term effects of cannabis on the brain specifically, Murat Yücel, Ph.D., M.A.P.S., of ORYGEN Research Centre and the Melbourne Neuropsychiatry Centre at the University of Melbourne, Australia, and colleagues from the University of Wollongong examined 15 men, with an average age of 39.8 years, who had smoked more than five joints daily for more than ten years. These were compared to 16 individuals, with an average age of 36.4 years, who were not cannabis users. The team performed a series of tests on the subjects, including high resolution structural magnetic resonance images, verbal memory tests, and assessment for subthreshold symptoms of psychotic disorders such as schizophrenia and mania.
In cannabis users, two major parts of the brain were generally smaller than in their straight counterparts: the hippocampus and the amygdala. The former is presumed to regulate emotions and memory, and was on average 12% smaller. The latter is related to fear and aggression, and was an average of 7.1% smaller in the users. Cannabis users also showed more sub-threshold symptoms of psychotic disorders. The authors commented on the verbal learning skills shown by the subjects, but this did not seem to correlate with the brain volume differences in either group.
The authors conclude with a call for more research in this area: "There is ongoing controversy concerning the long-term effects of cannabis on the brain," they write. "These findings challenge the widespread perception of cannabis as having limited or no neuroanatomical sequelae. Although modest use may not lead to significant neurotoxic effects, these results suggest that heavy daily use might indeed be toxic to human brain tissue. Further prospective, longitudinal research is required to determine the degree and mechanisms of long-term cannabis-related harm and the time course of neuronal recovery after abstinence."
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