Marijuana's effects on young brains diminish 72 hours after use, research says – CNN

The meta-analysis, published Wednesday in the journal JAMA Psychiatry, combines data from 69 previous studies that look at the effects of heavy cannabis use on cognitive functioning in adolescents and young adults. It found that those young people who identified as heavy marijuana users scored significantly lower than non-users in a variety of cognitive domains such as learning, abstraction, speed of processing, delayed memory, inhibition and attention. “There have been a couple of meta-analyses done in adult samples, but this is the first one to be done specifically in adolescent and young adult samples,” said Cobb Scott, assistant professor of psychiatry at the Perelman School of Medicine at the University of Pennsylvania and a lead author of the study. “We looked at everything from learning and memory to different aspects of executive functioning such as abstraction ability,” Scott said. “And we basically showed that the largest effects — which was around a third of a standard deviation — was in the learning of new information and some aspects of executive functioning, memory and speed of processing.”

But when the researchers separated the studies based on length of abstinence from marijuana use, the difference in cognitive functioning between marijuana users and non-users was no longer apparent after 72 hours of marijuana abstinence. That could be an indication “that some of the effects found in previous studies may be due to the residual effects of cannabis or potentially from withdrawal effects in heavy cannabis users,” Scott said. The study comes as America continues to debate the merits of marijuana legalization. Recreational marijuana use is legal in nine states. Twenty-nine states and the District of Columbia have legalized some form of medical marijuana use, with at least three additional states potentially deciding on the issue

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