Marijuana Use Linked to Poor Memory, Brain Abnormalities, Schizophrenia

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By Roshni Mahesh | December 17, 2013 1:08 AM EST

Smoking marijuana can leave a lasting impact on the brain, a new study says.

Researchers from the Northwestern University in the US found that youngsters who smoked marijuana regularly for three years had an abnormal brain structure and poor working memory. The damage persisted even two years after discontinuing the smoke. Additionally, the study also found a link between the marijuana-related brain abnormalities and the mental disorder schizophrenia.

Individuals afflicted with schizophrenia experience difficulty in differentiating the real from the unreal, thinking clearly, dealing with social situations normally and possessing normal emotional responses. The condition usually starts appearing during adolescence.

The study looked at 97 teens, aged between 16 and 17, including both non-smokers (44) and youngsters with marijuana use disorder (10), people with schizophrenia, with (15) and without (28) the history of smoking marijuana.

The participants underwent MRI scans of the brains, two years after quitting smoking. Researchers noticed brain abnormalities among the participants who smoked marijuana regularly, though they were not diagnosed with schizophrenia.

The study found that an early exposure left more negative impact on the brain regions related to memory. Memory-related structure of the brain was found shrunk among heavy users of marijuana.

Later, the participants gave some tests related to working memory. Heavy smoking was linked to a decline in working memory and performing badly in the memory tasks. "The study links the chronic use of marijuana to these concerning brain abnormalities that appear to last for at least a few years after people stop using it," lead study author Matthew Smith said in a news release.

Researchers also found solid evidence to prove the link between marijuana use and schizophrenia. Majority of the people affected with schizophrenia (90 percent) had a history of heavy smoking and started smoking marijuana early before they developed the disease. Apart from that, brain scans of the schizophrenia patients showed greater deterioration in the brain regions that help in learning, memory and play major role in maintaining communication between the brain regions.

"The abuse of popular street drugs, such as marijuana, may have dangerous implications for young people who are developing or have developed mental disorders," co-senior study author John Csernansky, said. "This paper is among the first to reveal that the use of marijuana may contribute to the changes in brain structure that have been associated with having schizophrenia."

The study will be reported in the journal Schizophrenia Bulletin.

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