The effects of chronic¹ marijuana use on the brain may depend on age of first use and duration of use, according to researchers at the Center for BrainHealth at The University of Texas at Dallas. In a paper published today in Proceedings² of the National Academy of Sciences (PNAS), researchers for the first time comprehensively describe existing abnormalities in brain function and structure of long-term marijuana users with multiple magnetic resonance³ imaging (MRI) techniques. Findings show chronic marijuana users have smaller brain volume in the orbitofrontal cortex (OFC), a part of the brain commonly associated with addiction⁴, but also increased brain connectivity.

 

"We have seen a steady increase in the incidence of marijuana use since 2007," said Dr. Francesca Filbey, Director of the Cognitive⁵ Neuroscience Research in Addictive⁶ Disorders⁷ at the Center for BrainHealth and Associate Professor in the School of Behavioral and Brain Sciences at The University of Texas at Dallas. "However, research on its long-term effects remains⁸ scarce despite the changes in legislation surrounding marijuana and the continuing conversation surrounding this relevant public health topic."

 

The research team studied 48 adult marijuana users and 62 gender⁹- and age-matched non-users, accounting¹⁰ for potential biases¹¹ such as gender, age and ethnicity. The authors also controlled for tobacco and alcohol use. On average, the marijuana users who participated in the study consumed the drug three times per day. Cognitive tests show that chronic marijuana users had lower IQ compared to age-and gender-matched controls but the differences do not seem to be related to the brain abnormalities as no direct correlation¹² can be drawn¹³ between IQ deficits¹⁴ and OFC volume decrease.

 

"What's unique about this work is that it combines three different MRI techniques to evaluate different brain characteristics," said Dr. Sina Aslan, founder¹⁵ and president of Advance MRI, LLC and adjunct assistant professor at The University of Texas at Dallas. "The results suggest increases in connectivity, both structural¹⁶ and functional¹⁷ that may be compensating¹⁸ for gray matter losses. Eventually, however, the structural connectivity or 'wiring' of the brain starts degrading with prolonged marijuana use."

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