Cannabis use in adolescence has no impact on brain structure in adulthood

The danger of cannabis for the neuronal development of adolescents is a common argument among supporters of prohibition. However, according to a study of Drug and Alcohol Dependence, Cannabis use during adolescence is not associated with structural differences in the brain in adulthood.

Methodology and results

The study involved 1,000 men, who were asked to declare their cannabis use when they were aged between 13 and 19. This enabled the scientists to identify different trajectories of cannabis use among adolescents: non-consumers / infrequent users, regular users, users whose cannabis intake drastically increased during the study period (13 to 19 years), and very frequent chronic users. A subgroup of the men studied (181 of them) then underwent structural neuroimaging in adulthood, when they were on average between 30 and 36 years old. Participants were grouped according to their cannabis trajectory, so that researchers could check whether these groups showed differences in adult brain structure, in the 14 areas likely to be affected. The study concluded that the brain structure of men from different trajectory subgroups did not differ.

The article states «Even the men most exposed to cannabis in adolescence had similar subcortical brain volumes and cerebral cortical volumes and thickness in adulthood to men with virtually no exposure to cannabis in adolescence».

This study confirms another study, which had also found no no significant difference between the brain of a regular cannabis user and the brain of a non-user.

However, it is still advisable not to consume cannabis before the age of 17, according to a 2017 study. The risk of cognitive impairment is greatly reduced if moderate cannabis use begins after this age. On the other hand, early use (13 /14 years) would lead to several types of cognitive decline, although researchers remain cautious about the actual harmful effects of the substance.

Other drugs, on the other hand, seem to have more negative effects on the brain. Another study concluded that alcohol had more impact on the brain than cannabis, since alcohol, unlike cannabis, leads to a reduction in gray and white matter in the brain.