A long-term study out of New Zealand has found that teens using marijuana on a regular basis may suffer from lowered intelligence as adults. Researchers followed 1,037 individuals, born between 1972 and 1973, for nearly four decades, analyzing them for the effects of persistent marijuana use on neuropsychological functioning. The participants, approximately five percent of which began using marijuana as teenagers, were given IQ tests at age 14, before any had begun using the drug, and again at 38, and were additionally surveyed at ages 18, 21, 26, and 38 about their drug use.
The study found that those who had smoked pot at least four times a week throughout the study suffered, on average, a loss of eight IQ points as adults. Researchers said that the intelligence loss did not appear to be associated with other factors such as the use of other drugs or alcohol, or the educational achievement of the participants.
The study also found a loss of intelligence quotient among participants who had stopped their use of marijuana sometime during the study. When researchers tested these participants at the age of 38, they found that their IQs were lower than at the beginning of the study, indicating that a cessation of pot smoking did not reverse the damage done earlier by the drug. By contrast, participants who began smoking marijuana as adults suffered either a minimal or no drop in intelligence or functioning.
“Researchers hypothesize that cannabis affects the hippocampus and prefrontal cortex, where learning, memory, and planning occur,” reported ModernMedicine.com, “and that teenagers are more susceptible to marijuana’s effects on the brain than older adults. They say their study highlights the importance of refraining from cannabis use during adolescence and the need for policies that encourage teenagers to stop using the drug altogether.”
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