Personal Health

Media Leaping to Extremely Faulty Conclusions from Study on the Effects of Marijuana on the Brain

Uh oh -- new study looks at brain imaging of marijuana consumers, but it's impossible to draw conclusions.

A new study identifying minor differences in the brain imaging of habitual marijuana consumers compared to non-users may be ideal for stimulating sensational headlines (e.g., “Regular pot smokers have shrunken brains, study says,” Los Angeles Times, November 10), but tells us little in regard to whether pot poses actual health risks.
Specifically, an MRI scan revealed less gray matter in the orbital frontal cortex of pot-smoking subjects compared to those who had never used the drug. Researchers also identified increased connectivity between certain regions of the brain in regular marijuana users compared with non-users.  
So precisely what do these findings tell us in regard to pot use and health? Not much. Since the study design is not longitudinal, investigators cannot determine whether these differences are caused by subject’s cannabis use, whether these differences existed prior to subjects’ ever trying cannabis, or whether these differences persist when users’ cannabis consumption ceases.
Most importantly, investigators in this study failed to determine whether any of these differences are positively associated with any measurable adverse performance outcomes, such as cognitive performance or quality of life. It may be that these cannabis users are functioning in their daily lives in a manner that is indistinguishable from controls, in which case the imaging differences may hold little if any real-world significance. (In fact, one of the paper’s authors acknowledged,  “[C]hronic users appear to be doing fine.”)
Authors’ comments in regard to marijuana-using subjects' IQs also need to be taken with a grain of salt. Researchers noted that marijuana users in the study possessed, on average, lower IQs than those in the non-using group, a finding they acknowledged may be linked to a variety of factors other than pot use. This outcome would hardly be surprising. A review of a highly publicized 2012 study purporting to link adolescent pot use to lower IQ later in life determined that once economic variables were factored into the assessment, cannabis’ actual effect on intelligent quotient was likely to be “zero.” The findings of a previous longitudinal study from Canada that tracked the IQs of a group of marijuana users and non-users from birth similarly concluded, “[M]arijuana does not have a long-term negative impact on global intelligence.”

Even if we are to accept the findings of this latest paper at face value, such concerns are hardly a justification for cannabis’ continued criminalization. Ultimately, if we are truly concerned about pot’s potential impact on the brain, and in particular how it may impact the developing brains of young people, the obvious public policy response is to regulate the substance in a manner that better restricts adolescents’ access to it and provides them with evidence-based information in regard to its potential risks. This is the policy we have employed for alcohol and tobacco, two substances that possess known risks far greater than those posed by cannabis, and they have been successful, as adolescent alcohol and tobacco use now stand at historic lows. It's high time we as a society employ a similarly principled policy for cannabis.

Paul Armentano is the deputy director of NORML (National Organization for the Reform of Marijuana Laws) and serves as a senior policy advisor for Freedom Leaf, Inc. He is the co-author of the book, Marijuana Is Safer: So Why Are We Driving People to Drink? (Chelsea Green, 2013).

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