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

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(CBS/AP) Teens who smoke marijuana frequently are more likely to experience a long-term drop in their IQ, according to a new study.

That could be a potential pitfall for millions of teens, given recent estimates show about one in 10 teens in grades nine through 12 smoke marijuana at least 20 times per month. The researchers however didn't find the same IQ dip for people who became frequent users of pot after 18, suggesting pot use is especially dangerous for the developing brain.

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

More than 1,000 study participants from New Zealand were tested for IQ at age 13 - likely before any significant marijuana use - and again at age 38. All were born in the town of Dunedin during a year-long span ending in 1973.

In addition to IQ tests, participants were given five interviews between ages 18 and 38, including questions related to their marijuana use. At age 18, 52 participants said they had become dependent on marijuana, meaning that they continued to use it despite its causing significant health, social or legal problems. Ninety-two others reported dependence starting at a later age.

Researchers compared their IQ scores at age 13 to the score at age 38 and found a drop only in those who had started regularly smoking pot by 18. Those deemed marijuana-dependent in three or more surveys had a drop averaging 8 points. If a person had average intelligence and was smarter than 50 percent of the population, dropping 8 points would give them a score only higher than 29 percent of the population, the researchers said.

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.

The study was published online Monday in the Proceedings of the National Academy of Sciences. It was funded with governmental grants from the United States and Britain, and a foundation in Zurich.

The researchers also surveyed people who knew the study participants well at age 38 and 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.

Dr. Richie Poulton, a study co-author and professor of developmental psychopathology at the University of Otago in New Zealand, said the message of the research is to stay away from marijuana until adulthood if possible. "For some it's a legal issue, but for me it's a health issue," he said.

Marijuana use is fairly common in American teens, as evidenced in a June government study that showed 23 percent of high school students said they'd recently smoked pot, surpassing cigarettes in popularity.

Young people "don't think it's risky," said Dr. Staci Gruber, director of the cognitive and clinical neuroimaging core at the Harvard-affiliated MacLean Hospital's Brain Imaging Center in Belmont, Mass. Gruber, who didn't participate in the new work, said the idea that marijuana harms the adolescent brain is "something we believe is very likely," and the new finding of IQ declines warrants further investigation.

Experts said the new research is an advance because its methods avoid criticisms of some earlier work, which generally did not measure mental performance before marijuana use began.

Dr. Nora Volkow, director of the National Institute on Drug Abuse which helped fund the research, said the research was "the cleanest study I've ever read" that looked long-term harm from marijuana use.

Ken Winters, a psychiatry professor at the University of Minnesota and senior scientist at the Treatment Research Institute in Philadelphia who wasn't involved in the study, said the new findings aren't definitive, but they underscore the importance of studying how marijuana may harm young people.

"Marijuana is very dangerous drug to the brain, particularly in adolescence, and it's also a carcinogen, so it's not healthy for adults either," Dr. Harris Stratyner, vice president of Caron Treatment Centers' New York Clinical Regional Services, told HealthDay. "It's much more dangerous than we've ever given it credit for."

[nb12345]

And Alcohol??? How is that working for you?

[rpowell002]

Seriously. Just regulate with an age mandate! If studies have shown (again, where are those studies in this article, by the way?) that smoking cannabis decreases IQ (also by the way, I'll take being smarter than 29% of the American population over 0%, [if my IQ has been lowered] given the idiotic corporate slaves who run this country)in those who have smoked it before the age of 18, just legalize it like the voters want, tax it like alcohol for (billions of dollars of) state/federal revenue, and create laws saying those under 18 (or 21-- whatever) can't buy it without ID that proves otherwise. By saying nobody can have it (i.e. prohibition), you make everyone want it, and they're always going to find a way to get it if they want it. Laws can only do so much, but if it's all we've got, it's all we've got. Congress, stop blinding yourselves to the people. If cannabis is legalized, I can guarantee there will be smarter, more aware people in this country, as opposed to the lazy, ignorant slobs who say they love being free, take another swig of their cheap, tax-able beer, and then go home to cause domestic disputes. If that's what Congress wants, that is-- which it doesn't. All these anti-pot movements are just further evidence that we live in a corporatocracy, controlled by the alcohol, tobacco, prison, and pharamaceutical industries. All I can do is continue to shake my head.

[D8627]

Where is the actual study? I can't find it anywhere. All these articles about this subject reflect on this study, I would think that one might have a link to it or something. Also, the only thing that they talk about that could affect the IQs is marijuana use, they don't talk about alcohol use or any other drug use. Another thing is that the average IQ DROP was 8 points. I'm not saying that this is the case, but the way it's worded, it could mean that all of the participants' IQ scores went up, except for one that dropped by 10, and one that dropped by 6. It's just kind of weird that all of these articles mention the same numbers and variables, and no more. I want to see the actual study.

[Lena_Butler]

Lower IQ is just one of the side effects of marijuana. There are a whole host of others that are dangerous and unpleasant.

http://www.testcountry.com/infographics/side-effects-of-using-marijuana.html

[2L82H8]

You really think you'll see the legalization of MJ or other harder drugs. This country can't even handle alcohol let alone anything else. By not legalizing Pot the government solves the problem of keeping you where they want you. And that's safe in your home. They have you in your place. Unfortunately, your insistence on doing this also means that you keep yourself at your home where you're out of harms way to yourself or to anyone else. Maybe if you had those 8 Extra IQ points you'd realize that you are a slave to your own habit.

[flboy1234]

dont really understand your logic,So if the goverment keeps it illeagal, youll stay in your house?And if its leagal ,that would also lead to staying in your house right where they want you.
Hmmmmmm,sounds like if anybody needs 8 more points its you.
Oh and 17 states including Washington D.C. (where our goverment resides) it has been decriminalized for medical use.You can spout off all you want why you dont like marijuana,The fact is your narrow mindednes has put blinders on you,you see states decriminalizing it every other month and your scared.And your scared from all the misinformation you insist on taking as fact.Hell you probably still think it causes people to rape and pillage.
I award you no points and everybody is now dumber for having read your post

[zooneedles]

Apparently Katy Lake would like to see an ordinance preventing the possession of anything valuable within the premises of local business properties in her area (cough, cough). What logic!

Admit it Katy you're being a bigot, plain and simple. You just want to make sure folks don't alter their consciousness on substances you and your zealot temperance associates don't like. You want everybody to think just like you, don't you honey?

Never going to happen, the Entheogen Community is here to stay.

[SallyLu27]

I know several people who smoked pot when we were teenagers, including my brother. I never enjoyed it, so was never a smoker. I am now 47 years old, and those friends of mine who smoked have vivid recollections of our childhood and teen years. My brother is one of the smartest people I know. He was at the top of his class in college with a double major and went through law school on an academic scholarship. I, on the the other hand, have a terrible memory. I only have flashes of memories from my past life, and even when someone says, don't you remember, giving me details, I often don't remember. I have a hard time remembering stuff that happened weeks ago. Are these things related? I don't know. But I often wonder if I would have been a smoker back in those days, would I have a better memory?

[casualtysr]

It's likely that those of us who used cannabis that had a bit of cannabidiol in it were completely unharmed and possible even gained some cognitive benefit from it. CBD is neuroprotectant and mitigates THC. Unfortunately over the last 20 years or so a lot of the strains were bred for even more THC which reduces CBD levels to nothing. There is a revival movement going on to bring CBD rich strains back into the fold but it takes time. Research has shown that CBD can kill cancer cells and can protect the brain from damage caused by ischemia. It even protects your brain from suffering damage caused by alcohol hangovers lol.

[kevin_hunt]

"said Dr. Nora Volkow, director of the National Institute on Drug Abuse, which helped fund the research."

NIDA scientist Dr. John Huffman created the new "synthetic marijuana" menace. Should we really trust any studies funded by NIDA? Their primary goal seems to be creating new dangerous drugs to replace old safe ones.

[flboy1234]

i do believe that it is illegal for any institute or goverment agency in america to fund any research for marijuana because its a schedule 1 drug.It is listed as having no medical value therfore no studys will be funded for any research in america.
As stupid as this sounds its the excuse our goverment feeds us.

[flboy1234]

I stand corrected.I found an article that states exactly that the us goverment helped fund the research.It also said that 52 of 1000 people became dependant by age 18.The article goes on to say that the subjects had an iq test at age 18 and 38,the conclusion was that there was only a drop in iq with the people that became dependant by age 18.
So 52 of 1000 people had a drop in iq.I can find 1000 people and test in the same way without marijuana being involved and get the same if not more of the same conclusion.
My conclusion is your iq will drop if you choose to believe this smoke and mirror show

[drewman5000]

No matter if you advocate the use of marijuana or not. You MUST give your brain a chance to grow before using any narcotic on any kind of repetitive basis.

[honestabe8]

I agree. Pot should be legal, but with the same restrictions as alcohol

[adansmith87]

Smokers in their thirties and forties have a heart attack rate that is five times higher than their nonsmoking peers. Cigarette smoking may be directly responsible for at least 20% of all deaths from heart disease.

foods that fight cancer || http://www.pinkkitchen.info/c4yw-inspired-me-cancer-will-not-beat-me/

[waldo5651]

i think the ones with the "lower iq's" are the ones who did this study and whoever wrote this article.