Cognitive Functioning in Abstinent Cannabis Users: A Neuropsychological and MEG Investigation

Cannabis is the most commonly used illicit substance worldwide, with an estimated 4% of the global population using cannabis annually. Considering the increasing legalisation of recreational and medicinal cannabis, usage rates are expected to rise, thus it is of utmost importance to understand how cannabis affects the brain and whether it is associated with long-term negative side effects. There is ample evidence linking both acute and chronic cannabis use with impairments on a range of memory and executive functions. However, what remains unknown is how pervasive these deficits are, and whether there is potential recovery with long-term abstinence. The current study sought to investigate the cognitive status of abstinent middle and older adult cannabis users, on both a behavioural and neurobiological level. A sample of past cannabis users (frequent n = 5; infrequent n = 6) and drug-naïve controls (n = 11) completed a battery of neuropsychological tests to measure behavioural performance, while a further subset of cannabis users (n = 3) completed functional neuroimaging (magnetoencephalography; MEG) to investigate potential subtle alterations to underlying neural activation. Broadly, it was hypothesised that previous cannabis users would perform worse on neuropsychological measures and display altered patterns of neural activity compared to controls. Analyses revealed no significant differences between abstinent cannabis users and controls on any neuropsychological measure, nor did they display altered brain activity. These findings lend support to a body of evidence that suggests cannabis-related deficits to cognition are not enduring and may recover with abstinence. Although further research is required to substantiate these findings given the limited sample size, the current results have important implications for our understanding of the effects of cannabis on the brain, and the potential for cognitive recovery.