Frequent Marijuana Use Bad for Teens’ Brains

Multiple Sources – August 10, 2014

At the American Psychological Association’s 122nd Annual Convention, psychologists discussed the health implications of legalizing marijuana which in part included the effect of marijuana on teens. Generally, psychologists agreed that smoking marijuana just once weekly can have significant negative effects on the brains of teens and young adults. Such effects include, cognitive decline, poor attention and memory, and decreased IQ (APA, 2014).

Krista Lisdahl, Ph.D., director of the brain imaging and neuropsychology lab at the University of Wisconsin-Milwaukee said, “It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neuro-cognitive damage, especially in youth.”

She continued that marijuana use is increasing, referencing a 2012 study of 1,037 participants who were followed from birth to age 38. This study found that 6.5% of high school seniors reported smoking marijuana daily, up from 2.4% percent almost 20 years earlier in 1993. Additionally, 31% of young adults between the ages of 18 and 25 reported using marijuana in the last month, while people who are addicted to marijuana can lose an average of six IQ points by adulthood.”

Lisdahl also stated that “Brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly among adolescents. Abnormalities in the brain’s gray matter, which is associated with intelligence, have been found in 16 to 19 year-olds who increased their marijuana use in the past year.” she said.

She further specified that, “These findings remained even after researchers controlled for major medical conditions, prenatal drug exposure, developmental delays, and learning disabilities.” Regarding legalization, she stated, “When considering legalization, policymakers need to address ways to prevent easy access to marijuana and provide additional treatment funding for adolescent and young adult users.” She further recommends that legislators consider regulating the levels of tetrahydrocannabinol, or THC, the major psychoactive chemical in marijuana, to help reduce potential neurocognitive effects.

Alan Budney, Ph.D., of Dartmouth College stated, “Some legalized forms of marijuana have higher levels of THC than other strains,” and noted that “THC is responsible for most of marijuana’s psychological effects.” Budney continued, “Past research has shown that frequent use of high potency THC can increase the risk of future problems with depression, anxiety, and psychosis. Recent studies suggest that this relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance.

Unfortunately, much of what we know from earlier research is based on smoking marijuana with much lower doses of THC than are commonly used today.”

According to Bettina Friese, Ph.D., of the Pacific Institute for Research and Evaluation in California, “People’s acceptance of legalized medical marijuana use appears to have an effect on adolescents’ perception of the drug’s risks, and presented results from a 2013 study of 17,482 teenagers in Montana, which found marijuana use among teenagers was higher in counties where larger numbers of people voted to legalize medical marijuana in 2004. In addition, teens in counties with more votes for the legalization of medical marijuana perceived marijuana use to be less risky.”

She pointed out that, “These findings suggest that a more accepting attitude toward medical marijuana may have a greater effect on marijuana use among teens than the actual number of medical marijuana licenses available.”


Feldstein Ewing, S. W., McEachern, A. D., Yezhuvath, U., Bryan, A. D., Hutchison, K. E., & Filbey, F. M. (2013). Integrating brain and behavior: Evaluating adolescents’ response to a cannabis intervention. Psychology Of Addictive Behaviors, 27(2), 510-525. doi:10.1037/a0029767

Maslowsky, J., Schulenberg, J. E., & Zucker, R. A. (2014). Influence of conduct problems and depressive symptomatology on adolescent substance use: Developmentally proximal versus distal effects. Developmental Psychology, 50(4), 1179-1189. doi:10.1037/a0035085

For more information, please feel free to contact me.

Wishing you well,


Material Provided as a Courtesy by: Matthew Dash, LCSW | DASH GROUP, LLC | 8 Maple Street, Suite 9 | Port Washington, NY 11050 | 516.232.8582 | | You may print or download Content from the Site for your own personal, non-commercial, informational or scholarly use, provided that you keep intact all copyright and other proprietary notices. Portions of material included within are copyrighted and utilized by permission from the author(s). Other portions are © 2010 – 2014 Dash Group, LLC. All Rights Reserved. For more information see Terms & Conditions.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDervis 3.0 Unported License.

Public Domain Mark

Leave a Reply

Your email address will not be published. Required fields are marked *