Twins study finds no evidence that marijuana lowers IQ in teens

Jan 19, 2016

Roughly half of Americans use marijuana at some point in their lives, and many start as teenagers. Although some studies suggest the drug could harm the maturing adolescent brain, the true risk is controversial. Now, in the first study of its kind, scientists have analyzed long-term marijuana use in teens, comparing IQ changes in twin siblings who either used or abstained from marijuana for 10 years. After taking environmental factors into account, the scientists found no measurable link between marijuana use and lower IQ.

“This is a very well-conducted study … and a welcome addition to the literature,” says Valerie Curran, a psychopharmacologist at the University College London. She and her colleagues reached “broadly the same conclusions” in a separate, nontwin study of more than 2000 British teenagers, published earlier this month in the Journal of Psychopharmacology, she says. But, warning that the study has important limitations, George Patton, a psychiatric epidemiologist at the University of Melbourne in Australia, adds that it in no way proves that marijuana—particularly heavy, or chronic use—is safe for teenagers.

Most studies that linked marijuana to cognitive deficits, such as memory loss and low IQ, looked at a single “snapshot” in time, says statistician Nicholas Jackson of the University of Southern California in Los Angeles, lead author of the new work. That makes it impossible to tell which came first: drug use or poor cognitive performance. “It’s a classic chicken-egg scenario,” he says.

To continue reading the entire article, click the name of the source below.

One comment on “Twins study finds no evidence that marijuana lowers IQ in teens”

  • Blockquote George Patton, a psychiatric epidemiologist at the University of Melbourne in Australia, adds that it in no way proves that marijuana—particularly heavy, or chronic use—is safe for teenagers.

    Isn’t this the guy who has been advocating that cannabis is harmful in Oz?

    Besides, the question is a general one: does it affect IQ and cognition? A/ Generally there is no evidence that it does. But if you add “chronic use”, well hell! Any chronic use of anything tends to be bad for anyone. Chronic alcohol consumption, chronic (normal) tobacco smoking, chronic eating, chronic fast food eating, chronic sex, chronic video game playing, chronic exercising, chronic everything is harmful.

    And then there is “normal” use of substances that cause harm: alcohol, according to the latest tv ads in Oz, suggest that even normal consumption of alcohol is harmful, causes cancer, strokes, etc.. The question is then, why is alcohol still legal. The answer is because prohibition did not work and made the problem worse with crime.

    The solution is simple (it is just the lack of political willingness to dare to change the world what is hindering change): legalize it. If there are health problems for some individuals, treat them as health and social problems, and not as offences.



    Report abuse

Leave a Reply

View our comment policy.