Cannabis link to IQ loss criticised
Tue, 15 Jan 2013 11:00a.m.
By Malcolm Ritter with 3 News online staff
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 analysis says the statistical analysis behind that conclusion is flawed.
The original study, reported last August, included more than 1,000 people who'd been born in Dunedin. Their IQ was tested at ages 13 and 38, and they were asked about marijuana use periodically between those ages.
Researchers at Duke University and elsewhere found that participants who'd reported becoming dependent on pot by age 18 showed a drop in IQ score between ages 13 and 38. The findings suggest pot is harmful to the adolescent brain, the researchers said.
Not so fast, says an 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 nothing to do with pot. Rather, it may have emerged from differences among the study participants in socioeconomic status, or SES, which involves factors like income, education and occupation, he says.
He based his paper on a computer simulation. It traced what would happen to IQ scores over time if they were affected by differences in SES in ways suggested by other research, but not by smoking marijuana. He found patterns that looked just like what the Duke study found.
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.
The Duke scientists, who learned of Rogeberg's analysis late last week, say they conducted new statistical tests to assess his proposed explanation. Their verdict: It's wrong. Rogeberg says they need to do still more work to truly rule it out.
A senior lecturer at the University of Otago’s National Addiction Centre, Dr Simon Adamson, says the new findings highlight a potential flaw in the original study.
“It doesn’t disprove the findings of the New Zealand group, but it does cast a little bit of doubt on that,” he says.
He also agreed further research was needed before conclusions could be drawn.
“It’s still an important finding, but it’s not the final word. It’s suggestive that there is a relationship there, but it would benefit from further study.”
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 cause 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.
AP / 3 News
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6/02/2013 1:44:24 p.m.
18/01/2013 10:04:41 a.m.
By the very nature of the subject, "Cannabis" when in debate, that level playing field is instead a steep decline of dissinformation, politics, propaganda & ignorance. Once the govt take control re growing, distribution & taxation of the plant & once gangs no longer profit from the plant & the worry from the general population has abated, perhaps then the fearmongring, overmydeadbody brigade may relent and say OK, I was wrong. It works very well in Amsterdam.
17/01/2013 2:02:34 a.m.
REEFER MADNESS wrote:
Complete bollocks, absolute hypocrisy that tobaccohol is legal and pot isn't.
15/01/2013 8:11:30 p.m.
bart wakker wrote:
If only researchers would make as much effort trying to proove the dangers of carrots, cucumbers and other vegetables, I'm sure they would find links to the most horrible diseases.
It never ceases to amaze me, how concerned politicians are about my health when it comes to weed. So much they even want to "protect" me against myself, that they would ruin my life with criminal prosecution and records if they could...
15/01/2013 8:07:33 p.m.
BULLOCK! I study better now and have worked harder than ever the past two years and I consider myself a 'pot head'. Before i smoked canabis I was a restless, attention seeking under achiever.Thanks Mary Jane :)
15/01/2013 4:32:45 p.m.
I hope they took into account the possibility they also consumed alot of other drugs as well during that period, as one tends to do while going through that phase. Not that im saying its a gateway drug but that if one is already interested in using a drug for recreational use then they are more likely to try out other drugs as well.
15/01/2013 3:42:39 p.m.
Yes well thats what everyone said! Everyone could see the obvious flawes to such a study!!! Even other drug use wasn't included from what i read!! How about we focus on the studies linking canabis to fighting brain tumours or cancer? Many studies! Many facts! Don't just say no. we must look at and accept the scientific facts!
15/01/2013 12:22:38 p.m.
Steve d wrote:
They can do all the studies they like but we all know that smoking Pot from early teen years messes with the developing brain..I know alot of people that have been pot smokers since they were young and some/most of them are complete idiots.
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