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gewg_ writes:

Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (NORML), reports at AlterNet:

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.