Pubdate: Tue, 15 Jan 2013
Source: Herald, The (Everett, WA)
Copyright: 2013 Associated Press
Contact:  http://www.heraldnet.com/
Details: http://www.mapinc.org/media/190
Author: Malcolm Ritter, Associated Press
Page: A2

LINK BETWEEN POT SMOKING, IQ DROP CHALLENGED

NEW YORK - A new analysis is challenging a report that suggests 
regular marijuana smoking during the teen years can lead to a 
long-term drop in IQ.

The author of the new paper says pot might not have anything to do 
with the mental decline seen in the original study, and that other 
factors may be to blame.

The original study included more than 1,000 people who'd been born in 
the town of Dunedin, New Zealand. Their IQ was tested at ages 13 and 
38, and they were asked about marijuana use periodically between those ages.

Participants who said they were dependent on pot by age 18 showed a 
drop in IQ score between ages 13 and 38, according to researchers at 
Duke University and elsewhere. Their report, which got wide attention 
last August, suggested pot is harmful to the adolescent brain.

Not so fast, says the new analysis, published online Monday by the 
Proceedings of the National Academy of Sciences.

Ole Rogeberg of the Ragnar Frisch Center for Economic Research in 
Oslo, says the IQ trend might have emerged from differences among the 
study participants in socioeconomic factors like income, education 
and occupation.

He based his paper on a computer simulation. Drawing on results of 
earlier research, It traced the potential effects of those 
socioeconomic factors on IQ. He found patterns that looked just like 
what the Duke study found for smoking marijuana.

In an interview, Rogeberg said he's not claiming that his alternative 
explanation is definitely right, just that the methods and evidence 
in the original study aren't enough to rule it out. He suggested 
further analyses the researchers could do with their data.

The Duke scientists, who learned of Rogeberg's paper late last week, 
say they conducted new statistical tests that ruled out his explanation.

Rogeberg says they need to do still more work to truly rule it out.

Experts unconnected to the two papers said the Rogeberg paper doesn't 
overturn the original study. It "raises some interesting points and 
possibilities," but provides "speculation" rather than new data based 
on real people, said Dr. Duncan Clark, who studies alcohol and drug 
use in adolescents at the University of Pittsburgh.

Dr. Nora Volkow, director of the National Institute on Drug Abuse, 
said observational studies of people like the Duke work can't 
definitively demonstrate that marijuana causes irreversible effects 
on the brain. In an email, she said Rogeberg's paper "looks sound" 
but doesn't prove that his alternative explanation is correct either.
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MAP posted-by: Jay Bergstrom