Why Do You Think They Are Called Potheads?

Steven Dubovsky, MD


Journal Watch. 2008;7(7) 

Chronic heavy use is associated with low hippocampal volumes, psychopathology, and cognitive impairment.

Marijuana, long considered a benign illicit substance, has recently been associated with drug dependence, amotivational states, and, possibly, psychosis. Researchers in Australia used high-resolution MRI to examine cannabinoid-receptor–rich regions in the amygdala and hippocampus of 15 heavy cannabis users (mean daily use, 5–7 joints; mean duration of regular use, 20 years) and 16 nonusers. The participants, all men, did not meet criteria for DSM disorders; cannabis was the primary drug of abuse among users; and alcohol use was similar between groups.

Left and right hippocampus volumes were 12% smaller in cannabis users than in controls (effect size, 1.2); left and right amygdala volumes were 6% and 8% smaller, respectively (effect sizes, 0.8 and 1.0). Marijuana smokers had significantly more depressive, positive, and negative symptoms as measured by standard rating scales, and poorer performance on a test of auditory learning. Cumulative cannabis exposure was inversely associated with left hippocampal volume, which in turn was inversely associated with positive symptoms.

The study method could not clarify whether an action on cannabinoid receptors in these regions reduced synaptic density or the number or size of neurons or glial cells (all such reductions have been reported in animal studies). Whatever the mechanism, heavy chronic marijuana use appears to be associated with volume loss; subsyndromal psychotic, negative, and depressive symptoms; and cognitive impairment.

These participants were not psychiatrically ill and used other substances minimally, which suggests that the findings are not associated with an emerging illness but with neurotoxicity of marijuana. Patients who use the drug should be informed about its risks.

— Steven Dubovsky, MD

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