Early marijuana use may lead to abnormal brain function and lower IQ, according to researchers from London and Ontario, Canada. The research team says that young users could suffer from abnormal brain function in brain areas related to visuo-spatial processing, memory, self-referential activity and reward processing.

“Many youth in our program use marijuana heavily and, despite past research, believe it improves their psychiatric conditions because it makes them feel better momentarily,” says Elizabeth Osuch, a Scientist at Lawson Health Research Institute, the Dr. Joseph Rea Chair in Mood Disorders at the Schulich School of Medicine & Dentistry at Western University as well as the Medical Director of the First Episode Mood and Anxiety Program (FEMAP) at London Health Sciences Center. “For this reason, we decided to study the effects of marijuana and depression on psychiatric symptoms, brain function and cognitive function.”

The research team studied four groups consisting of youths. The groups included depressed youths who do not use marijuana, depressed youths who use marijuana frequently, youths who are not depressed but used marijuana frequently and healthy youths who are not marijuana users.

The participants who were then divided into groups based on their marijuana use before the age of 17 also underwent brain scanning and psychiatric, cognitive and IQ tests. Overall, the team did not find evidence that using marijuana improves depression. The depressive symptoms were not different in depressed youths who used marijuana and depressed youths who did not.

Moreover, marijuana use did not correct brain function deficits of depression. In fact, its use even made the brain function deficits of some brain regions worse. The findings also show that early marijuana use is associated with low IQ.

Meanwhile, Osuch and researchers from Western University’s Robarts Research Institute found that the gene that produces Brain Derived Neurotropic Factor (BDNF), which is involved in brain development and memory, was more abundant in early marijuana users. This could indicate that a genetic variation may lead young people to use marijuana at an early age. However, this study is limited and needs to be verified in a larger study.