Peter Suciu for redOrbit.com – Your Universe Online

A new study from Northwestern University has raised serious concerns for those backing the recent push to decriminalize marijuana. Study researchers found unhealthy changes in the brain structures of heavy marijuana users, changes that resemble those found in the brains of individuals with schizophrenia.

The study looked at daily marijuana use that began between the ages of 16 to 17 and lasted for about three years. At the time of the study, participants had not been using marijuana for about two years.

“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,” said study author Matthew Smith, an assistant research professor in psychiatry and behavioral sciences at Northwestern University. “With the movement to decriminalize marijuana, we need more research to understand its effect on the brain.”

The study cohort included 97 subjects: healthy controls, subjects with a marijuana use disorder, people with schizophrenia but no history of a marijuana use disorder and schizophrenic patients with a marijuana use disorder.

Ninety percent of the 15 marijuana smokers who had schizophrenia in the study began using marijuana heavily before they showed signs of the mental disorder. The researchers also found that marijuana-related brain abnormalities are linked to a poor working memory performance, according to their report in the journal Schizophrenia Bulletin.

“The abuse of popular street drugs, such as marijuana, may have dangerous implications for young people who are developing or have developed mental disorders,” said study author Dr. John Csernansky, chair of psychiatry and behavioral sciences at Northwestern University. “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.”

Researchers conducted a structural MRI on participants to correlate abnormalities in these regions with working memory, the ability to remember and instantly process information. While previous research has found effects of marijuana on the cortex, few studies have looked at chronic marijuana use in otherwise healthy people and individuals with schizophrenia, the researchers noted.

The team found that memory-related structures in the brains of chronic users appeared to shrivel and collapse inward, perhaps due to a decrease in neurons. While all of the chronic users in the study showed evidence of brain alterations, subjects with schizophrenia had more significant deterioration in the thalamus, a key structure for learning, memory and communications between brain regions.

The study team added that chronic marijuana use could boost the underlying process driving schizophrenia.

“If someone has a family history of schizophrenia, they are increasing their risk of developing schizophrenia if they abuse marijuana,” Smith said.

“A tremendous amount of addiction research has focused on brain regions traditionally connected with reward/aversion function, and thus motivation,” noted study author Dr. Hans Breiter, a professor of psychiatry and behavioral sciences at Northwestern. “This study very nicely extends the set of regions of concern to include those involved with working memory and higher level cognitive functions necessary for how well you organize your life and can work in society.”

“If you have schizophrenia and you frequently smoke marijuana, you may be at an increased risk for poor working memory, which predicts your everyday functioning,” Smith said.

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