Early Marijuana use is associated with low IQ, says study

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Early Marijuana use

Marijuana use becomes more common nowadays. However, studies show that it can increase risks for mental illness, such as major depressive disorder, bipolar disorder, and schizophrenia, particularly in early users.

In a recent study, scientists find that early marijuana use leads to brain network change and is associated with cognitive deficits. The finding is published in Acta Psychiatrica Scandinavica.

Researchers from University of Western Ontario in Canada, Lawson Health Research Institute in Canada, Robarts Research Institute in Canada, St. Joseph’s Hospital in Canada, and Brain and Mind Institute in Canada conducted the study.

They examined cognitive function, functional brain network, and genetic risk with major depressive disorder alone and combined with marijuana use, and differences among early, late, or non- Marijuana use in youth.

A total of 74 young adults in 4 groups were studied: people in the healthy control group, people with major depressive disorder, people who frequently use marijuana, and people who has/had major depressive disorder plus frequent marijuana use.

Researchers examined participants’ psychiatric symptoms, cognitive performance, and demographics. They also scanned participants with fMRI technique to measure the functional brain network, and evaluated the risk alleles in six genes of interest.

The result showed that Brain network differences among 4 groups in brain regions related to reward and motor control. Moreover, the effects of marijuana use and major depressive disorder were different.

Early marijuana use was associated with lower IQ and hyperconnectivity within areas of the brain network. In addition, early marijuana use was associated with the BDNF (Brain-derived Neurotrophic Factor) risk allele.

Researchers suggest that cognitive deficits linked with early marijuana use are present within several years after marijuana use began and may result from, or share a common cause with early-onset marijuana use.

Moreover, the brain network can be affected by major depressive disorder, marijuana and their combination, as well as by early marijuana use. BDNF carrier state may predispose to early marijuana use.


Citation: Osuch EA, et al. (2016). Depression, marijuana use and early-onset marijuana use conferred unique effects on neural connectivity and cognition. Acta Psychiatrica Scandinavica, published online. DOI:10.1111/acps.12629.
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