Does marijuana lower IQ? New study challenges link

Gary Parrish smokes marijuana in a glass pipe, Thursday, Dec. 6, 2012, just after midnight at the Space Needle in Seattle when marijuana use was legalized in the state. A new study is challenging a previously found link between marijuana use and IQ reductions teens. / Ted S. Warren

NEW YORK Smoking pot regularly as a teen may lead to lower IQ scores by adulthood, a recent study showed.

Or maybe not -- according to the authors of a new analysis challenging that research.

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

The original study, published Aug. 26 in Proceedings of the National Academy of Sciences (PNAS), 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.

"Parents should understand that their adolescents are particularly vulnerable,'" lead study author Madeline Meier, a postdoctoral researcher at Duke University's Center for Child and Family Policy, said at the time.

However, the new analysis -- published Jan. 14, also in PNAS -- found other differencse among the study group including their education, occupation and other socioeconomic factors may have contributed to the drop in IQ.

Study author Ole Rogeberg of the Ragnar Frisch Center for Economic Research in Oslo, based the new research on a computer simulation. Drawing on results of earlier studies, 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.

• Smoking marijuana regularly as a teen may lower IQ scores as an adult

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, disagree and said they conducted new statistical tests that ruled out his explanation.

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

As the researchers debate, 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.

Marijuana is the most commonly used illegal drug in the world, according to NIDA, and causes short-term effects such as euphoria, distorted perceptions, memory impairment, and difficulty thinking and solving problems.

A government survey from U.S. Substance Abuse and Mental Health Services Administration (SAMHSA) found about 7 percent of Americans ages 12 and up were current marijuana users.

Recreational marijuana use was recently legalized in Colorado and Washington following the November elections.

[ribbiereber]

I smoked habitually in my teens and twenties, then went a couple of decades with only rare encounters. Then I tested out and qualified to join Mensa in my 50s. Based on the premise being discussed here, I would have been another freakin' Einstein if I'd never discovered the Evil Weed. But I can live with that.

[Live_in_Faith]

Or the studies are bogus and you would had scored a lower IQ, but due to your marijuana use you gained an inquisitive mind that helped you solve problems "outside the box" and you scored higher in IQ in your 50's.

[Mr_Jackson]

Ha i wonder if this was done by the same people who tried to say marijuana kills brain cells. For those of you that do not know the study that was done to prove THC kills brain cells has been debunked. They connected mask to monkey's and pumped in pure THC, no oxygen. What happens when the brain doesn't receive oxygen? Thats right brain cells die.

[magnumdr]

corse not i smoked it many yers and it didnot bothar me ane bit.

[eroteme2]

It may have affected your spelling and your use of lower case i instead of capital I.

[bobbychuckles]

To quote Robin Williams as Mork "Oh! Humour! Haha!"

[eroteme2]

Lower IQ? May be difficult to discern being users begin at the low end.

[Cannabinoids_Treat_Autism]

Oh dear, not done your research have you?

Studies have found that cannabis users tend to have higher IQ's than non-users.

Also, 8% of employed people (that means people with a job) take illegal drugs. Only 2% of unemployed people take illegal drugs.

[Live_in_Faith]

I am sure you have had a beer, which is more harmful that marijuana. I would say there are high IQ and Low IQ people that like marijuana. But the high IQ people like it more than alcohol because instead of dumbing you down, it tends to make you think deeper about concepts, situations, and how to make things more effecient. At least it does for me.

[jimbo7776]

It is hard to find good unbiased research on cannabis use. Unrestricted access to high potency cannabis as is the situation for Colorado medical marijuana patients right now is unprecedented. Thalidomide, which appeared safe until we had a number of patient-years of use is the ultimate cautionary tale. If you use cannabis either medicinally or recreationally, please do it safely, discreetly and moderately.

[bobbychuckles]

There's simply no comparison between Cannabis and Thalidomide.
Cannabis has been used safely for thousands of years. Thalidomide was only briefly tested in Europe and the effects were documented almost instantaneously with its' introduction.
Potency is a complete non-issue. Users simply self-titrate dosage to achieve the desired result. Strains with a high level of Cannabidiol(CBD) actually regulate themselves, due to the fact that CBD inhibits THC absorption.

[bobbychuckles]

Who better than the 'experts' at Duke University do we need to explain this?
They were founded by big Tobacco and fought for years to deny the link between cigarettes and cancer.
You have to pity the poor prohibitionists these days. They spend most of their time grasping at straws and find most of the research that upholds their claims disintegrate faster than a saltine in a vat of battery acid.
Pot impairs cognition. That's why Carl Sagan stated publicly that it helped him with complicated equations and theorems, I guess.
It causes lung cancer and bronchitis. Must be the reason why Dr. Donald Tashkin found quite the opposite, after thirty years of research.
Pot will turn you into a Schizophrenic. Nice try, but the evidence against that is everywhere you look.

[He-is-able]

It doesn't cause schizo- or does it- it doesn't- well maybe it could- naah it don't- but then again you never know...

[raymailhot]

The real discovery was the stupid kids are the ones that like it?

[bobbychuckles]

The stupid kids drank Bourbon and grew up to be Republicans.

[Live_in_Faith]

3 of those "stupid kids" grew up and became President. Although one never inhaled or "never had sexual relations with that woman" either.
The question is not "is pot perfect?" The question is it worth the cost, corruption, and violence caused by its prohibition?

If you think it is, you just flunked an IQ test yourself.

[Noval53]

It's pointless to debate the good or bad points about a substance that's illegal to thoroughly study. Industrial hemp is also illegal even though the seed (in food form) is quite legal and beneficial to eat. What lowers America's IQ in general, is the failed prohibition and war against the "evil weed".

[ealohagirl]

Not only is your ignorance showing. Where you abused as a child? Is it easier to be a sloth and not educate yourself? Those that live in glass houses tend to throw alot of stones and all it accomplishes is revealing the fact that you have a serious Mental Disorder. YOU ARE A BULLY - GET HELP

[robert_holt]

does smoking pot decrese your iq i donnow. i only smoked it for a while but that led me to harder stuf. does the harder stuf decrese my iq i donnow. what are we talking about again? what am i doing here? oh damn it theres that pink elefant again.

[Mr_Jackson]

The only reason you moved to harder stuff is because its illegal in the first place. Where do most people who use marijuana get it from? A drug dealer. When you go to the liqueur store do they offer you some drug that they just got in? No? Same would be true if marijuana was legal and regulated.

[Faramir0028g]

A long time ago my pop, RIP, showed me study of how bad pot was, the study said pot made monkeys crazy. A year or 2 later I was in a dorm and our adviser was one of the graduate assistants on that study, the poor monkeys were smoking pot all day long 10 joints apiece 30-40 lb. monkeys. Yeah they went crazy but a test about how moderate cannabis use affects people no not really.
Most of the studies done by the government on weed are junk science. They want to prove something not find the truth.