New Evidence of a Link Between Marijuana Use and Schizophrenia?

According to researchers, habitual users of America’s favorite illicit drug may also be at-risk for memory loss and other brain abnormalities. 

By: James Swift
UncommonJournalism@gmail.com
@UNJournalism

While impressive sales have many legalized marijuana shop owners in Colorado feeling euphoric, that same exuberance isn't being shared by some in the scientific community.

Last month, a report published in the journal Schizophrenia Bulletin indicated that habitual teenage users of marijuana -- defined as individuals who used the drug, on a daily basis, for around three years -- demonstrated abnormal brain structure changes, most notably pertaining to the users’ working memory.

Researchers at Northwestern University studied subjects in their early 20s, who reported cessation of marijuana use for at least two years. According to their findings, the abnormalities were still present, perhaps indicating long-term damage stemming from their prior use of the drug. These brain structure changes -- which may portend the possible decrease of neurons -- are also likely to reflect brain function changes, the authors of the study suggest.

“We found that individuals with a past history of daily marijuana use, who were otherwise healthy, demonstrated impaired working memory compared to healthy individuals without a history of substance abuse,” said Dr. Matthew J. Smith, lead author of the study and a research assistant professor at the Feinberg School of Medicine’s Department of Psychiatry and Behavioral Sciences. “We observed that the shapes of brain structures related to working memory seemed to collapse inward…the marijuana-related differences observed in the shape of these brain structures were directly related to the participants’ impaired performance on working memory tasks.”

Using MRI to observe the subcortical gray matter of nearly 100 subjects, researchers said the severity of the brain abnormalities hinged on the age in which individuals began using marijuana. Regions of the brain associated with working memory, they said, may be more susceptible to potential negative drug effects depending on how early users began regularly smoking marijuana.

Habitual use of the drug, researchers said, may also play a factor in the development of schizophrenia-like symptoms. Approximately 90 percent of subjects participating in the study who had schizophrenia -- representing 15 out of the 97 individuals within the total population -- said they began using marijuana heavily prior to developing the disorder.

“We observed a similar pattern of working memory impairment among individuals with schizophrenia who also had a past history of daily marijuana when compared to individuals with schizophrenia without a history of substance abuse,” Smith said. As the study was gathered at one point in time, however, he said two possible explanations for the findings may exist.

“The first is that the past history of daily marijuana use causes the observed brain differences,” Smith said. “Alternatively, these differences may have already existed before marijuana use began, and as such, they may be biological markers of a vulnerability to marijuana misuse or poorer working memory.”

The study found that heavy marijuana users with schizophrenia displayed more severe deterioration of the thalamus -- a brain structure significant for learning and memory -- than other subjects. Furthermore, the authors of the report said the new data suggests that regions of the brain central to higher cognitive functions may be negatively impacted by heavy marijuana use.

“In this study we observed that the group with the past history of marijuana use and who were otherwise healthy, were characterized by inward shape deformations in the front and top of the thalamus,” Smith said. “The thalamus is involved with cognitive functions, for example working memory, as well as sensory signals, for example, vision and hearing.”

Although Smith said more research is necessary to better grasp the full neuroscientific implications of teenage marijuana use, he believes the potential negative effects of the drug on the developing young mind may be enough to warrant greater state interventions.

“At the least, given that adolescent brain development is vulnerable to the effects of marijuana and other substances such as alcohol,” he concluded, “great care should be taken to regulate the availability in states where it is legal.”

Uncommon Journalism, 2014.