Link between teen pot smoking and lower IQs questioned

A young woman sports funky marijuana-themed glasses at Toronto's annual 420 smoke off. (Nathan Denette/Canadian Press)


A Norway-based researcher is raising questions about a widely-covered 2012 report that suggested teens who regularly smoke marijuana could see a long-term drop in their IQ.

Research led by Duke University post-doctoral researcher Madeline Meier, which CBC News reported on in August 2012, suggested teens who frequently smoke pot may suffer long-term damage to their brains - especially those who start smoking young.

• Teenage pot smoking tied to loss of IQ

But on Monday, the Proceedings of the National Academy of Sciences (PNAS) published the online version of an analysis challenging the Duke scientists' conclusions. Oslo-based researcher Ole Røgeberg suggests the drop in IQ may have stemmed from other differences among the study participants, including their socioeconomic status.

He argues that the causal effects estimated in the Meier-led study are "likely to be overestimates, and that the true effect could be zero."

The original study tested the IQ of over 1000 young people from the town of Dunedin, New Zealand at ages 13 and 38. Between those tests, the young participants were periodically asked about their use of marijuana.

Those who self-identified as being dependent on pot by the age of 18 saw a drop in their IQ scores, one of the findings that suggested marijuana negatively affects brain development.

But Røgeberg argued that the original study should have taken other factors into consideration, like the participants' economic status and level of education. Using a computer simulation, he modeled how other variables could have hampered the young peoples' IQ scores.

The Duke scientists, who are aware of the analysis, believe their more recent statistical tests rule out Røgeberg's argument - but the Oslo-based researcher continues to call for further scrutiny of the link.

Independent observers - like youth substance use researcher Dr. Duncan Clark at the University of Pittsburgh - say that although Røgeberg's computer-driven analysis doesn't negate the original study, it does raise "some interesting points and possibilities."

As researchers debate the link between pot smoking and brain development, we are wondering how much attention teenagers are paying to the discussion.

Do you have a young person in your life who seems concerned over where scientists stand on smoking pot?

If you smoked marijuana as a teenager, how much did you understand about its potential effects?
 

 



(This survey is not scientific, results are based on readers' replies.)

Related:

• Teenage pot smoking tied to loss of IQ
• CBC readers react to teen pot smoking study