Marijuana Use Does Not Cause Brain Abnormalities

An important study from the Journal of Neuroscience shows that marijuana use does not cause structural brain changes.
By Fred Gardner On November 23, 2015
marijuana does not cause brain damage
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Originally published in O’Shaughnessy’s

Dr. Dale Deutsch forwarded an important study from the Journal of Neuroscience showing that marijuana use does not cause structural brain changes. This is a reversal of the conventional wisdom—a Tashkin-level expose. (UCLA pulmonologist Donald Tashkin and colleagues reported in 2005 that smoking marijuana does not cause lung cancer.) And just as Tashkin’s findings were buried by the biomedical establishment and corporate media, so, too, has the paper by Barbara J. Weiland and colleagues at the University of Colorado and the University of Louisville—published in January—been conspicuously ignored.

Reviewing the papers purporting to show that marijuana use alters brain morphology, Weiland et al note serious inconsistencies:

“Marijuana use has been associated with both increased (Cousijn et al., 2012) and decreased (Yücel al., 2008; Demirakca et al., 2011; Solowij et al., 2011) volumes of subcortical structures, or both (Battistella et al., 2014).”

And a serious limitation:

“Importantly, these studies were not designed to determine causality (i.e., that marijuana use causes morphological changes), which would require a longitudinal design to establish temporal precedence.”

Moreover, the conventional wisdom is based on studies that:

“…did not adequately exclude the effects of confounding variables. Several reports included marijuana groups that differed from control groups in alcohol use/abuse (Demirakca et al., 2011; Solowij et al., 2011; Schacht et al., 2012; Gilman et al., 2014). Unlike marijuana, alcohol abuse has been unequivocally associated with deleterious effects on brain morphology and cognition in both adults (Sullivan, 2007; Harper, 2009) and adolescents (Nagel et al., 2005; Medina et al., 2008; Squeglia et al., 2012). Statistically controlling for comorbid alcohol abuse, as many studies do, is not an ideal strategy, especially in small groups or under conditions where covariates may interact with the independent variable (Miller and Chapman, 2001). Thus, it is possible that alcohol use, or other factors, may explain some of the contradictory findings to date.”

Yet, studies reporting brain damage have all been widely publicized by the mass media and accepted as Scientific Truth.  

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Revision date: 
Nov 23, 2015