title: Weighing the Evidence: A Systematic Review on Long-Term Neurocognitive Effects of Cannabis Use in Abstinent Adolescents and Adults.
abstract: Findings on neurocognitive effects of sustained cannabis use are heterogeneous. Previous work has rarely taken time of abstinence into account. In this review, we focus on understanding sustained effects of cannabis, which begin when clinical symptoms of the drug have worn off after at least 14 days. We conducted a search between 2004 and 2015 and found 38 studies with such a prolonged abstinence phase. Study-design quality in terms of evidence-based medicine is similar among studies. Studies found some attention or concentration deficits in cannabis users (CU). There is evidence that chronic CU might experience sustained deficits in memory function. Findings are mixed regarding impairments in inhibition, impulsivity and decision making for CU, but there is a trend towards worse performance. Three out of four studies found evidence that motor function remains impaired even after a time of abstinence, while no impairments in visual spatial functioning can be concluded. Functional imaging demonstrates clear differences in activation patterns between CU and controls especially in hippocampal, prefrontal and cerebellar areas. Structural differences are found in cortical areas, especially the orbitofrontal region and the hippocampus. Twenty studies (57 %) reported data on outcome effects, leading to an overall effect size of r mean = .378 (CI 95 % = [.342; .453]). Heavy use is found to be more consistently associated with effects in diverse domains than early age of onset. Questions of causality-in view of scarce longitudinal studies, especially those targeting co-occurring psychiatric disorders-are discussed.
authors.affiliation: Deutsches Zentrum für Suchtfragen des Kindes- und Jugendalters (DZSKJ; German Center for Addiction Research in Childhood and Adolescence), University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246, Hamburg, Germany. f.ganzer@uke.de.
authors.forename: Florian
authors.initials: F
authors.lastname: Ganzer
authors.affiliation: Deutsches Zentrum für Suchtfragen des Kindes- und Jugendalters (DZSKJ; German Center for Addiction Research in Childhood and Adolescence), University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246, Hamburg, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Bröning
authors.affiliation: Deutsches Zentrum für Suchtfragen des Kindes- und Jugendalters (DZSKJ; German Center for Addiction Research in Childhood and Adolescence), University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246, Hamburg, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Kraft
authors.affiliation: Deutsches Zentrum für Suchtfragen des Kindes- und Jugendalters (DZSKJ; German Center for Addiction Research in Childhood and Adolescence), University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246, Hamburg, Germany.
authors.forename: Peter-Michael
authors.initials: PM
authors.lastname: Sack
authors.affiliation: Deutsches Zentrum für Suchtfragen des Kindes- und Jugendalters (DZSKJ; German Center for Addiction Research in Childhood and Adolescence), University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246, Hamburg, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Thomasius
mesh_terms: D000293:Adolescent; D000328:Adult; D002188:Cannabis; D006801:Humans; D002189:Marijuana Abuse / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000523:psychology*
keywords: Cannabis; Cognitive effects; Marijuana; Neuropsychology; Systematic review; THC