According to a new study, any neurological effects caused by cannabis use are only statistically significant in the immediate days after termination. Amy M. Schreiner of the Department of Psychology at the University of Central Florida recently led a study that looked at 33 existing meta-analyses of cognitive impairment experienced by heavy cannabis users. The goal of the study was to determine whether the negative effects of cannabis use, such as memory impairment, attention, and executive functioning issues persist after use has stopped. Tetrahydrocannabinol (THC), a main component of cannabis, is believed to be the leading cause of these negative effects. Because THC remains in the fat cells of an individual long after it has been ingested, researchers have questioned whether it can continue to deliver negative influences days and weeks after its ingestion.
Schreiner chose to focus on studies that involved heavy cannabis users who had stopped using for a period of time. Thirteen of her studies included users who had abstained for 25 days, while the others had shorter abstinence periods. This allowed her to review a number of factors contributing to the negative symptoms. For instance, those experiencing withdrawal may have had additional problems with anger, irritability, anxiety, or even depression as a result of stopping their drug use. However, when Schreiner examined all of the variables and reviewed all the studies, she was unable to prove that the residual effects of cannabis caused cognitive impairment.
When Schreiner looked at studies that included heavy cannabis users evaluated during states of extreme intoxication, she found some statistical impairments in memory, learning, and attention. But she was unable to provide evidence of long-lasting impairment. Specifically, the participants demonstrated no significant cognitive deficiencies once the intoxication period ended. The study did demonstrate some negative effects on motor functioning and verbal skills as well, but these were also minimal after intoxication. Schreiner added that even though some of her findings were statistical, they may not have been clinically significant and may have had little or no effect on the practical functioning of the individuals. Additionally, Schreiner found no symptoms of impairment in the individuals who had abstained for 25 days. In conclusion she said, “These results fail to support the idea that heavy cannabis use may result in long-term, persistent effects on neuropsychological functioning.”
Schreiner, A. M., Dunn, M. E. (2012). residual effects of cannabis use on neurocognitive performance after prolonged abstinence: A meta-analysis. Experimental and Clinical Psychopharmacology. Advance online publication. doi: 10.1037/a0029117
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