Abstract
The growing concern about cannabis use, the most used illicit drug worldwide, has led to an increase in the number of cannabis studies using neuroimaging techniques to determine its effect on brain structure and function. We conducted a systematic review to assess the evidence of the impact of chronic cannabis use on brain structure and function in adults and adolescents. Papers published until August 2012 were included from EMBASE, Medline, PubMed and LILACS databases following a comprehensive search strategy and pre-determined set of criteria for article selection. Only neuroimaging studies involving chronic cannabis users with a matched control group were considered. One hundred and forty-two studies were identified, of which 43 met the established criteria. Eight studies were in adolescent population. Neuroimaging studies provide evidence of morphological brain alterations in both population groups, particularly in the medial temporal and frontal cortices, as well as the cerebellum. These effects may be related to the amount of cannabis exposure. Functional neuroimaging studies suggest different patterns of resting global and brain activity during the performance of several cognitive tasks also in both groups, which may indicate compensatory effects in response to chronic cannabis exposure. The results pointed out methodological limitations among studies and high heterogeneity in the findings. Chronic cannabis use may alter brain structure and function in adult and adolescent population. Further studies should consider the use of convergent and multimodal methodology, prospective large samples involving adolescent to adulthood subjects, and data-sharing initiatives. Grants: PNSD/2011/050, PNSD2006/101, SGR2009/1435.
Highlights
Cannabis is the illicit drug most widely available and used worldwide [1,2], consumed by between 125 and 203 million people, largely younger age group (15–34 years), which corresponds to an annual prevalence rate of 2.8%–4.5% [1,2]
These effects are probably related to effects on the endocannabinoid system, which can modulate the neuronal activity of other neurotransmitter systems, such as dopamine, through its action on the most abundant cannabinoid receptor in brain, the cannabinoid receptor 1 (CB1) [16,17]
CB1 receptors mature slowly, reaching maximal levels during adolescence [18], and are concentrated in brain regions that are critical for executive functioning, reward processing and memory, such as the prefrontal cortex, anterior cingulate cortex, basal ganglia, medial temporal areas and cerebellum [19]
Summary
Cannabis is the illicit drug most widely available and used worldwide [1,2], consumed by between 125 and 203 million people, largely younger age group (15–34 years), which corresponds to an annual prevalence rate of 2.8%–4.5% [1,2]. Cannabis use has been associated with a range of acute and chronic mental health problems, such as anxiety, depression, neurocognitive alterations and deficits as well as increased risk of psychotic symptoms and disorders, the severity of these effects being dependent on frequency of use, age of onset and genetic vulnerability [5,6,7,8,9,10,11,12,13,14,15]. We conducted a systematic review to assess the evidence of the impact of chronic cannabis use on brain structure and function in adults and adolescents
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