While cognitive performance is negatively affected by cannabis use, the negative effects appear to completely wear off within a month, according to research published in the Experimental and Clinical Psychopharmacology in late June.
"With the number of cannabis users both illicitly and licitly increasing, the question of any potential lasting impact from cannabis use is increasingly important," Amy M. Schreiner and Michael E. Dunn of the University of Central Florida wrote in their study.
Numerous studies have found that cannabis use affects memory, attention, perceptual-motor tasks, and other cognitive processes, but studies on how long these effects last has been inconsistent. The studies were complicated by the fact that psychoactive compounds in marijuana can linger in the body for days.
In hopes of better understanding the long-term, lasting effects of cannabis use, the researchers used a meta-analysis, a statistical procedure that allows researchers to mathematically summarize the results of a number of different studies.
Schreiner and Dunn's study included two of these meta-analyses. The first was comprised of 33 studies that examined the cognitive effects of cannabis use after intoxication had worn off. The second was comprised of 13 studies that also examined the cognitive effects of cannabis use after intoxication had worn off, but this group of studies tested users after at least 25 days of abstinence.
The study found that cannabis use caused small impairments in attention, learning, and other cognitive processes that persisted after intoxication. However, the researchers said it was unclear if these minor impairments "translate[d] into practical impairments in functioning." But the second meta-analysis suggested that these minor impairments don't last longer than a month.
"While the first meta-analysis revealed a small significant negative effect for general performance and a number of cognitive domains, the clinical significance remains unclear," Schreiner and Dunn explained. "A second meta-analysis focusing on studies with longer abstention periods was conducted and indicated no lasting residual effects on neurocognitive performance as a result of cannabis use... Whether differences seen in the initial days or weeks of abstinence are due to drug residue effects or withdrawal effects, after approximately 1 month these effects do not persist for the moderate to heavy user."
[Marijuana leaf via Shutterstock]