Among participants who’d been dependent at 18 and in at least one later survey, quitting didn’t remove the problem. IQ declines showed up even if they’d largely or entirely quit using pot at age 38, analysis showed.
The researchers got similar overall results for IQ decline when they compared participants who reported having used marijuana at least once a week on average for the past year. The researchers had no data on how much was used on each occasion or how potent it was.
Dr. Duncan Clark, a researcher at the University of Pittsburgh, said he’s not convinced that mental decline is only in those who become dependent by age 18. He said the main lesson he sees in the overall study results is that to preserve one’s IQ, it’s best to avoid marijuana entirely, no matter what your age.
The researchers also surveyed people who knew the study participants well at age 38. They found that the more often participants were rated as marijuana-dependent in the surveys over their lifetimes, the more memory and attention problems were noticed by their acquaintances over the previous year.
Perry reported from Wellington, New Zealand.
By Andrew P. Napolitano
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