Marijuana Doesn’t Lower IQ, Except in the Media

Back in 2012, when a Duke University study purported to find a link between chronic marijuana use and IQ decline in teenagers, the mainstream media treated the findings like a dire warning from on high — the definitive last word on the subject, and a troubling impediment for anyone thinking of legalizing the drug for adults. Meanwhile, those of us who understand the way government-funded research tends to drastically over-inflate the dangers of cannabis looked into the details, and found as usual, some troubling questions remained unanswered.

For starters, with only 38 people in the study, how reliable could the results be? And what efforts were made to eliminate other confounding factors in IQ loss besides marijuana?

Then, six months after the study came out, the Proceedings of the National Academy of Sciences of the United States — the same journal that published it, offered a new take — this time questioning the way the Duke researchers drew their conclusions. Ultimately, the journals editors stated flatly that “although it would be too strong to say that the results [of the Duke study] have been discredited, the methodology is flawed and the causal inference drawn from the results premature.”

Needless to say, that bold declaration didn’t draw .01% of the media attention that the original, fear-mongering headlines drew. Nor has a new study from the University College of London that offers far more data on the subject of teen marijuana use and IQ scores than the previous Duke study, with decidedly different results.

According to the Washington Post:

The study draws on a considerably larger sample of adolescents than the Duke research – 2,612 children born in the Bristol area of the U.K. in 1991 and 1992. Researchers examined children’s IQ scores at age 8 and again at age 15, and found “no relationship between cannabis use and lower IQ at age 15,” when confounding factors – alcohol use, cigarette use, maternal education, and others – were taken into account. Even heavy marijuana use wasn’t associated with IQ.

“In particular alcohol use was found to be strongly associated with IQ decline,” the authors write. “No other factors were found to be predictive of IQ change.”

Of course, if you’re waiting for an apology from the mainstream media for breathlessly reporting government-funded, highly skewed marijuana research without looking into the details, for the millionth time, don’t hold your breath. Going that long without oxygen will definitely lower your IQ score!