Skip to main content

The Globe and Mail

Does pot smoking really lower teens' IQs? A new study begs to differ

It turns out the recent finding that pot smoking as teenagers makes for dopey adults may not have been such smart research after all.

A new analysis of the data suggests that researchers may have missed a more significant social factor than an adolescent marijuana habit: poverty.

The first study, as the Los Angeles Times reports, looked at the large cohort of New Zealanders who were followed from birth to their late 30s. It found that those who smoked marijuana as teens had IQs that were five to six points lower at age 38 than those who had not indulged or only smoked infrequently. The latter group was found to score marginally better on the tests.

Story continues below advertisement

The findings made sense: Developing research suggests that the teenage brain, at an important stage of development, may be particularly susceptible to drugs and alcohol.

Now Norwegian research suggests the first study may have missed a more salient influence: social economic status, which predisposes kids to both early marijuana use and less cognitively stimulating environments. The study, which was written by Ole Rogeberg from the Ragnar Frisch Centre for Economic Research in Oslo, points out that kids with higher IQs, and those from more affluent family environments, are significantly less likely to start pot smoking earlier or do it heavily. The Los Angeles Times article reports that based on his assessment, Rogeberg concludes that once you consider the "self-selecting" aspect of early, heavy pot-smokers – low-income, less stimulating environments, a range of IQs, and poorer life prospects – the "true effect" of teenaged marijuana use "could be zero."

Properly assessing the role of socioeconomic status on intelligence, life outcomes and illness is an ongoing challenge for researchers. The impact of poverty can often hide within the data. Consider research that came out last year that suggested that low-income moms were being diagnosed with higher rates of generalized anxiety disorder not because they were clinically more predisposed to anxiety, but because they were anxious about paying the bills.

Researchers concluded that helping them financially and offering parenting classes would go further to reducing anxiety than traditional therapies and medication.

Similarly, the Norwegian study, which will no doubt be the subject of further debate, suggests that public policies may be looking in the wrong place. Yes, it's better to caution teens against spending their high school years stoned. But if the only consequence, on average, to rich kids is a few IQ points (and even that might be suspect, and have little impact on life outcomes), a more effective focus would be specifically targeting the kids who are disadvantaged by economic circumstance beyond their control. The real problem here is poverty.

Report an error Licensing Options
About the Author

Erin Anderssen writes about mental health, social policy and family issues. More


The Globe invites you to share your views. Please stay on topic and be respectful to everyone. For more information on our commenting policies and how our community-based moderation works, please read our Community Guidelines and our Terms and Conditions.

We’ve made some technical updates to our commenting software. If you are experiencing any issues posting comments, simply log out and log back in.

Discussion loading… ✨