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Marijuana and the brain

News — Posted 22/04/14

New research shows marijuana use may cause schizophrenia-like brain changes.

The harmfulness of marijuana is a contentious topic, but two recent studies have added to the debate with evidence that regular cannabis use may lead to abnormal brain structure changes, similar to those experienced by schizophrenic patients.

Casual marijuana use impacts emotion and motivation brain centres

For one study conducted at Northwestern University in Illinois,researchers used different methods of neuroimaging to examine brains of casual marijuana users and non-users aged 18 to 25. Specifically, they looked at the volume, shape and density of grey matter in the nucleus accumbens and the amygdala, important regions for emotion and motivation.

This is the first study to show that recreational use of marijuana is related to major brain changes. It also showed that the degree of brain abnormalities in these regions is directly related to the amount of marijuana a person smoked each week. That is, the more a person smokes, the more abnormal changes are likely to occur.

“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” said co-senior study author, psychiatrist Dr Hans Breiter. “People think a little recreational use shouldn’t cause a problem, if someone is doing okay with work or school. Our data directly says this is not the case.”


“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences.”


Long-term use can create changes similar to schizophrenic patients

Long-term use of marijuana has also been linked to "concerning brain abnormalities that appear to last for at least a few years after people stop using it," according to assistant research professor in psychiatry Dr Matthew Smith, the lead researcher on another study on the effects of marijuana use.

This study, also conducted at Northwestern University in Illinois, looked at MRI scans of young adults who began smoking marijuana regularly at the age 16 or 17 and continued for around three years. The scans revealed deterioration in the thalamus of the brain, an area important for learning, memory and communication. At the time of testing, the participants had been marijuana-free for two years and were not using other drugs.

The researchers also noted that if a person has a family history of schizophrenia, marijuana use may increase their risk of developing the disorder.

"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," co–senior author Dr John Csernansky said.

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