Early marijuana use associated with abnormal brain function, study reveals

October 5, 2016
A dried flower bud of the Cannabis plant. Credit: Public Domain

In a new study, scientists in London, Ontario have discovered that early marijuana use may result in abnormal brain function and lower IQ.

Marijuana is the most commonly used illegal substance in the world. Previous studies have suggested that frequent marijuana users, especially those who begin at a young age, are at a higher risk for and , including depression, and schizophrenia.

Dr. Elizabeth Osuch, a Scientist at Lawson Health Research Institute and the Dr. Joseph Rea Chair in Mood Disorders at the Schulich School of Medicine & Dentistry at Western University, is a Canadian leader in studying both mood and anxiety disorders and the effects of marijuana.

"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," said Dr. Osuch, who is also the Medical Director of the First Episode Mood and Anxiety Program (FEMAP) at London Health Sciences Centre. "For this reason, we decided to study the effects of marijuana and depression on psychiatric symptoms, brain function and cognitive function."

Dr. Osuch and her team recruited youth in four groups: those with depression who were not marijuana users; those with depression who were frequent marijuana users; frequent marijuana users without depression; and healthy individuals who were not marijuana users. In addition, participants were later divided into youth who started using marijuana before the age of 17 and those who began using it later or not at all.

Participants underwent psychiatric, cognitive and IQ testing as well as brain scanning. The study found no evidence that marijuana use improved depressive symptoms; there was no difference in psychiatric symptoms between those with depression who used marijuana and those with depression who did not use marijuana.

In addition, results showed differences in brain function among the four groups in areas of the brain that relate to reward-processing and motor control. The use of marijuana did not correct the brain function deficits of depression, and in some regions made them worse.

Of additional interest, those participants who used marijuana from a young age had highly abnormal brain function in areas related to visuo-spatial processing, memory, self-referential activity and reward processing. The study found that early marijuana use was also associated with lower IQ scores.

"These findings suggest that using marijuana does not correct the brain abnormalities or symptoms of depression and using it from an early age may have an abnormal effect not only on brain function, but also on IQ," said Dr. Osuch.

With past research suggesting a genetic role between marijuana use and depression, Dr. Osuch and her collaborators at Western University's Robarts Research Institute also conducted genetic testing on participants. They discovered that a certain genetic variation of the gene that produces Brain Derived Neurotropic Factor (BDNF) was found in greater proportion in youth who used marijuana from an early age. BDNF is involved in brain development and memory, among other processes.

"This is a novel finding that suggests this genetic variation may predispose youth to early marijuana use," said Dr. Osuch. However, Dr. Osuch notes that this study had a small number of participants. These genetic results are therefore tentative and need to be verified with a larger study with more participants.

The study, "Depression, marijuana use and early-onset marijuana use conferred unique effects on neural connectivity and cognition", is published in the journal Acta Psychiatrica Scandinavica.  

Explore further: Study: Long-term marijuana use changes brain's reward circuit

More information: E. A. Osuch et al, Depression, marijuana use and early-onset marijuana use conferred unique effects on neural connectivity and cognition, Acta Psychiatrica Scandinavica (2016). DOI: 10.1111/acps.12629

Related Stories

Study: Long-term marijuana use changes brain's reward circuit

June 6, 2016
Chronic marijuana use disrupts the brain's natural reward processes, according to researchers at the Center for BrainHealth at The University of Texas at Dallas.

Marijuana brain study offers new substance by including nicotine use

October 2, 2015
Until recently, marijuana research largely excluded tobacco users from its participant pool. But scientists at the Center for BrainHealth at UT Dallas have found reason to include them, uncovering significant differences ...

Canada to allow medical marijuana patients to grow cannabis

August 11, 2016
The Canadian government says medical marijuana patients will be able to grow their own cannabis under new regulations that come into effect later this month.

Government won't reclassify marijuana, allows more research

August 11, 2016
The Obama administration isn't going to reclassify marijuana and remove it from the list of the most dangerous drugs.

Study finds nicotine changes marijuana's effect on the brain

August 18, 2015
How scientists study the effects of marijuana on the brain is changing. Until recently marijuana research largely excluded tobacco users from its participant pool, but scientists at the Center for BrainHealth at The University ...

Recommended for you

A walk at the mall or the park? New study shows, for moms and daughters, a walk in the park is best

November 17, 2017
Spending time together with family may help strengthen the family bond, but new research from the University of Illinois shows that specifically spending time outside in nature—even just a 20-minute walk—together can ...

Risk of distracted driving predicted by age, gender, personality and driving frequency

November 17, 2017
New research identifies age, gender, personality and how often people drive as potential risk factors for becoming distracted while driving. Young men, extroverted or neurotic people, and people who drive more often were ...

When male voles drink alcohol, but their partner doesn't, their relationship suffers

November 17, 2017
A study of the effect of alcohol on long-term relationships finds that when a male prairie vole has access to alcohol, but his female partner doesn't, the relationship suffers - similar to what has been observed in human ...

Spanking linked to increase in children's behavior problems

November 16, 2017
Children who have been spanked by their parents by age 5 show an increase in behavior problems at age 6 and age 8 relative to children who have never been spanked, according to new findings in Psychological Science, a journal ...

Multiplayer video games: Researchers discover link between skill and intelligence

November 15, 2017
Researchers at the University of York have discovered a link between young people's ability to perform well at two popular video games and high levels of intelligence.

Generous people give in a heartbeat—new study

November 15, 2017
Altruistic people are said to be "kind hearted" - and new research published in the journal Scientific Reports shows that generous people really are more in touch with their own hearts.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

walkon58
not rated yet Oct 05, 2016
No real information in the study. How many were involved in the experiment? What was the drop in IQ? How young is considered early? Really even the person doing the study admits that it is invalid due to the small number of people involved in the study. Basically just rubbish.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.