Study questions link between teen pot smoking and IQ decline

NEW YORK -- A new analysis is challenging the idea that smoking marijuana during adolescence can lead to declines in intelligence.

See Full Article

Instead, the new study says, pot smoking may be merely a symptom of something else that's really responsible for a brainpower effect seen in some previous research.

It's not clear what that other factor is, said Joshua Isen, an author of the analysis. But an adolescent at risk for smoking pot "is probably going to show this IQ drop regardless of whether he or she is actually smoking marijuana," said Isen, a lecturer in psychology at Loyola Marymount University in Los Angeles.

The study was released Monday by the Proceedings of the National Academy of Sciences. Some prior research has led to suggestions that the developing adolescent brain is particularly vulnerable to harm from marijuana.

Studying the topic is difficult because children can't ethically be randomly chosen to either take illicit drugs or abstain for years so that their outcomes can be compared. Scientists have to assess what people do on their own.

For the new work, the researchers examined data that had been collected for two big U.S. studies of twins. They focused on 3,066 participants who were given a battery of intelligence tests at ages 9 to 12 -- before any of them had used marijuana -- and again at ages 17 to 20.

They tracked changes in the test scores and studied whether those trajectories were worse for marijuana users than for non-users. Most tests revealed no difference between the two groups, but users did fare more poorly than abstainers in tests of vocabulary and general knowledge.

If smoking pot harmed test scores, the researchers reasoned, people who'd smoked more pot should show poorer trends than those who'd smoked less. But that's not what the data revealed. Among users, those who'd smoked more than 30 times or used it daily for more than a six-month stretch didn't do worse.

The study also looked at 290 pairs of twins in which one had used marijuana and the other had not. The members of each pair had grown up together and 137 sets were identical twins so they shared the same DNA. Again, the pot users did not fare worse than their abstaining twin siblings.

So, the researchers concluded, pot smoking itself does not appear responsible for declines in test scores. Isen noted, however, that the work says nothing about other potential harmful consequences of smoking marijuana in adolescence.

Dr. Nora Volkow, director of the National Institute on Drug Abuse, said that while the study has some limitations, it is important and deserves to be followed up with more research. She noted the government has already launched a project to follow about 10,000 children over time to assess the impact of marijuana and other drug use.

A prominent 2012 study had indicated long-term IQ harm from pot smoking in teenagers. An author of that research said the new work does not conflict with her finding. Terrie Moffitt of Duke University said her study dealt with marijuana use that was far more serious and longer-lasting than the levels reported in the new work.


Latest Tech & Science News

  • Forest tours offered in Chinese to promote conservation in B.C.

    Tech & Science CTV News
    VANCOUVER -- Conservationists have their eyes on a demographic that hasn't been tapped into before in terms of educating people about British Columbia's old growth forests. About half a million people in B.C.'s Lower Mainland are Chinese-language speakers, yet most environmental programs and tours are offered in English only, said Ken Wu, executive director of the Ancient Forest Alliance. Source
  • U.S. presidential election uses hodge-podge of voting technology

    Tech & Science CBC News
    When Americans go the polls on Nov. 8, they'll be casting votes using a wide array of technology, from touchscreens to pen and paper. In light of Donald Trump's claims of election fraud — and with the memory of the disputed presidential election of 2000 still looming — that technology could be under more scrutiny than ever in this year's presidential election. Source
  • Attacks that disrupted Twitter, Paypal, Spotify were just a dry run, hackers say

    Tech & Science CBC News
    Could millions of connected cameras, thermostats and kids' toys bring the internet to its knees? It's beginning to look that way. On Friday, epic cyberattacks crippled a major internet firm, repeatedly disrupting the availability of popular websites across North America and Europe such as Twitter, Netflix and PayPal. Source
  • Attacks on the internet getting bigger and nastier

    Tech & Science CTV News
    NEW YORK -- Could millions of connected cameras, thermostats and kids' toys bring the internet to its knees? It's beginning to look that way. On Friday, epic cyberattacks crippled a major internet firm, repeatedly disrupting the availability of popular websites across the United States. Source
  • Glenn Greenwald weighs in on WikiLeaks data dump on Clinton

    Tech & Science CBC News
    Two people at the heart of the most earth-shattering leaks of stolen data in the past few years are at odds about how those troves of documents should be handled in public. "You'd have to be a sociopath to think that we ought to just take all of this material and dump it all on the internet without regard to the impact that it will have for innocent people," says Glenn Greenwald, the journalist who first reported on the massive document leak provided to him by former U.S. Source
  • Alberta to spend more to cut methane emissions

    Tech & Science CTV News
    EDMONTON - Alberta plans to spend more money to cut methane emissions. Environment Minister Shannon Phillips says another $33 million will be added to the $7 million already pledged to reduce emissions of the greenhouse gas by 45 per cent by 2025. Source
  • 'Red Dead Redemption 2' - 3 ways it could fail [Photos]

    Tech & Science Toronto Sun
    Saddle up, pardner. It looks like we’re going back to the Wild West. Rockstar Games, the video game empire behind the juggernaut Grand Theft Auto series, set the Internet on fire this week by releasing mysterious images that suggest – nay, outright declare – another game in the Red Dead series is on its way. Source
  • Cyberattacks disrupt Twitter, Netflix, PlayStation Network, others

    Tech & Science Toronto Sun
    LONDON — Cyberattacks on a key Internet firm repeatedly disrupted the availability of popular websites across the United States on Friday, according to analysts and company officials. The attack had knock-on effects for users trying to access popular websites from across America, Canada and even in Europe. Source
  • Russian indicted on charges he hacked LinkedIn

    Tech & Science CTV News
    SAN FRANCISCO -- A Russian man has been charged with hacking and stealing information from computers at LinkedIn and other San Francisco Bay Area companies, federal prosecutors announced Friday. A grand jury indicted Yevgeniy Aleksandrovich Nikulin, 29, of Moscow, Russia, on Thursday on charges including computer intrusion and aggravated identity theft, the U.S. Source
  • Why it's so hard to land on Mars: Bob McDonald

    Tech & Science CBC News
    It looks more and more like the Schiaparelli lander crashed on Mars this week, a huge disappointment for the European Space Agency and the Russian space agency, Roscosmos. But the incident is only the last in a long history of robot missions to Mars, where almost 60 per cent have failed for one reason or another. Source