Duration of abstinence from cannabis is positively associated with verbal learning performance: A systematic review and meta-analysis.

Abstract

Although there is a consensus that cannabis intoxication will have deleterious effects on a wide spectrum of cognitive skills, there is no consensus regarding the duration of time from last use necessary to ameliorate these effects. A systematic review and series of meta-analyses were undertaken to assess anticipated gains in verbal learning with longer periods of cannabis abstinence. Studies assessing verbal learning performance in abstinent regular cannabis users and nonusing control participants; studies reporting length of cannabis abstinence at the time of neuropsychological assessment; and studies implementing one of three highly comparable measures of verbal learning and memory were included in the analyses. The included tasks have demonstrated some of the most robust declines associated with cannabis use and are prevalent in the clinical practice of neuropsychology. We assessed associations between cannabis abstinence and verbal learning scores via mixed effects subgroup analyses. Twenty-three studies (k = 28; N = 1,711) met all inclusion criteria. Cannabis users abstinent for 7 days or fewer performed worse than controls on verbal learning tasks, whereas cannabis users abstinent for longer periods showed no average significant difference in verbal learning performance compared with controls. Based on available evidence, some amelioration of verbal learning limitations presumed to result from cannabis appear to resolve between 7 and 28 days of sustained abstinence. However, in the reviewed studies, years of regular use were inversely related to longer periods of abstinence and verbal learning performance, undermining a confident inference that abstinence alone has direct benefits to verbal learning and memory. (PsycINFO Database Record (c) 2020 APA, all rights reserved).