Marijuana and Brain Development

How does one take the leap from this clip to marijuana use?  Crush’s description of Marlin’s journey through the “jellies” seems to be  the view of many  toward marijuana.  Laughing off “smoking a j” during high school and college with I “had some serious thrill issues.”

Thrill issues, risk taking or sensation-seeking are all attributes associated with the period between childhood and adolescence.  Usually risk-taking decreases between adolescence and adulthood.  (Although there are some people who are perpetual thrill seekers but they are in the minority.) What’s going on during this time period?

One review of the literature by Steinberg (2008) explains risk-taking as a feature of brain development.  Specifically risk-taking behavior occurs because of dramatic changes around the time of puberty in the dopaminergic system of the brain.  What’s this mean?  There are nerve cells in the mid brain called dopaminergic neurons that produce dopamine.  Dopamine is a chemical that controls voluntary muscle movement as well as mood, stress or experience of rewards, in fact quite an array of behaviors, including addiction.

Research suggests that the brain is not fully developed until age 25 (Lenroot, 2006). Between adolescence and adulthood (the fully developed brain) risk-taking behavior slows down as the dopamine system settles down.  This allows adults to self-regulate that is, think this through, control themselves, make considered choices.

Development is at a different pace for different people but these 15 or so years are important because of heightened vulnerability to recklessness.

So why have we taken this trip?  Because of a  study published this August in the Proceedings of the National Academy of Sciences.  This longitudinal study ,done in New Zealand, followed individuals from birth until they were 38 years old.  Participants took neuropsychological tests at ages 13 and again at age 38.  They were interviewed about their use of marijuana at ages 18, 21, 26, 32 and 38.

The findings were striking.  Those who used marijuana regularly, especially those who started using it as adolescents, showed a significant decline in IQ.  Additionally, family and close friends noticed the difference in their cognitive function.

So, where does this study take us?  Supporters of marijuana for casual use might say that IQ tests are questionable tools to base decisions on whether or not to use marijuana.  Others might point to a variety of other factors that might reduce people’s IQ, from environmental exposures to television or video gaming.

Though marijuana is an incredibly useful prescribed medication, this study may cause one to pause and wonder about it’s recreational use, especially during adolescence.  In the end, it is no laughing matter.

Kuehn, B. (2012).Marijuana Use Starting in Youth Linked to IQ Loss. JAMA.308(12):1196.

Lenroot, R. (2006).Brain development in children and adolescents: insights from anatomical magnetic resonance imaging. Neuroscience Biobehav Review 30(6):718-29.

Steinberg, L. (2008) A Social Neuroscience Perspective on Adolescent Risk-Taking
Developmental Review. 28(1): 78–106.