The 5 Biggest Lies About Pot—And How to Rebut Them

No, smoking marijuana doesn't lower your intelligence.

1. Consuming marijuana lowers intelligence.

“The best evidence is that you lose, if you use marijuana as a teenager regularly, eight IQ points. I don’t know about the rest of the table, but I don’t have eight (IQ points) to lose.” —Washington Post columnist Ruth Marcus, July 27, 2014

The source of this oft-repeated claim is a 2012 longitudinal study by Madeline Meier and colleagues that associated the persistent use of cannabis prior to age 18 with lower IQ at mid-life. However, a separate review of Meier’s data, published in the same journal, disputed any direct link between cannabis use and declined IQ. That review argued that Meier’s team had failed to properly control for potential confounding factors, such as subjects’ socio-economic status. After accounting for these variables, the author theorized that the “true effect (on early onset cannabis use and IQ) could be zero.”

More recent longitudinal studies further dismiss the notion that cannabis exposure negatively impacts IQ. A 2016 British study published in the Journal of Psychopharmacology assessed IQ and educational performance among a cohort of 2,235 marijuana-using teens and never users. Authors concluded, “[T]he notion that cannabis use itself is causally related to lower IQ and poorer educational performance was not supported in this large teenage sample.”

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