The nature of the teenage brain makes users of cannabis amongst this population particularly at risk of developing addictive behaviours and suffering other long-term negative effects, according to researchers at the University of Montreal and New York’s Icahn School of Medicine at Mount Sinai.

The researchers reviewed over 120 studies that looked at different aspects of the relationship between cannabis and the adolescent brain, including the biology of the brain, chemical reaction that occurs in the brain when the drug is used, the influence of genetics and environmental factors, in addition to studies into the “gateway drug” phenomenon. “Data from epidemiological studies have repeatedly shown an association between cannabis use and subsequent addiction to heavy drugs and psychosis (i.e. schizophrenia). Interestingly, the risk to develop such disorders after cannabis exposure is not the same for all individuals and is correlated with genetic factors, the intensity of cannabis use and the age at which it occurs. When the first exposure occurs in younger versus older adolescents, the impact of cannabis seems to be worse in regard to many outcomes such as mental health, education attainment, delinquency and ability to conform to adult role,” Dr Jutras-Aswad said.

Cannabis interacts with our brain through chemical receptors (namely cannabinoid receptors such as CB1 and CB2.) These receptors are situated in the areas of our brain that govern our learning and management of rewards, motivated behaviour, decision-making, habit formation and motor function. As the structure of the brain changes rapidly during adolescence (before settling in adulthood), scientists believe that the cannabis consumption at this time greatly influences the way these parts of the user’s personality develop.

The researchers stress that while a lot remains unknown about the mechanics of cannabis abuse, the body of existing research has clear implications for society. “It is now clear from the scientific data that cannabis is harmful to the adolescent brain, specifically those who are most vulnerable from a genetic or psychological standpoint. Identifying these vulnerable adolescents, including through genetic or psychological screening, may be critical for prevention and early intervention of addiction and psychiatric disorders related to cannabis use,” Dr Hurd said.