Cannabis neurotoxicity: analysis of structural neuroimaging data

Due to the current discussions regarding the regulation of cannabis consumption, an update of the data on its harmful effects appears to be warranted. One regularly used argument against a less restrictive regulation of cannabis has been its potentially toxic effect on the structure of the brain. A substantial number of specific neuroimaging studies have been published during the last two decades. In adults, no published studies have been able to find significant differences between cannabis users and control subjects regarding total brain volume, and grey or white matter volume. Positive results of analyses of cortex sections have regularly been contradicted by subsequent studies. The same conclusions can be drawn for adolescents as for adults: available studies show no difference in total volumes, and regional differences found in some studies are either not replicated or even contradicted by several other studies. It is worth noting that all these studies were cross-sectional and measured “a posteriori” brain volumes, i.e. subsequent to the beginning of cannabis use. Even when the results were consistently positive, no deduction of a causal link could be made. Given the available data, one cannot therefore maintain the hypothesis of a toxic effect of cannabis, which would result in negative alterations of brain volume. No preventive or repressive action may thus be grounded on the thesis of such a toxic effect.