August Newsletter

Teenage Marijuana Use May Hurt Future IQ

Please share this information with your teens! 


August 27, 2012  ABC News
Reported by Drs. Tiffany Chao and  Shari Barnett:

In a study of more than 1,000 adolescents in New Zealand, those who began habitually smoking marijuana before age 18 showed an eight-point drop in IQ between the ages of 13 and 38, a considerable decline. The average IQ is 100 points. A drop of eight points represents a fall from the 50th percentile to the 29th percentile in terms of intelligence.

The research, published in the Proceedings of the National Academy of Sciences, charted the IQ changes in participants over two decades.

The eight-point drop in IQ was found in subjects who started smoking in adolescence and persisted in “habitual smoking” — that is, using cannabis at least four days per week — in three or more of the five study waves. In contrast, those who never used marijuana at all gained nearly one IQ point on average.

Madeline Meier, lead researcher and a post-doctoral associate at Duke University, said that persistent use of marijuana in adolescence appeared to blunt intelligence, attention and memory. More persistent marijuana use was associated with greater cognitive decline.

“Collectively, these findings are consistent with speculation that cannabis use in adolescence, when the brain is undergoing critical development, may have neurotoxic effects,” Meier writes in the study.

“[The findings] provide evidence for the actual — rather than ideological and legal — basis for concerns regarding cannabis use,” said Dessa Bergen-Cico, a assistant professor of public health, food studies and nutrition at Syracuse University.  “These findings reinforce recommendations on the importance of primary prevention, evidence based drug education and policy efforts targeting not only adolescents, but elementary age children before they start.”

“Increasing efforts should be directed toward delaying the onset of cannabis use by young people,” writes Meier, “particularly given the recent trend of younger ages of cannabis-use. initiation in the United States and evidence that fewer adolescents believe that cannabis use is associated with serious health risk.”


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