By Steve Elliott
A new study from the University College of London of 2,612 children in the United Kingdom 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. Even heavy cannabis use had no associated with reduced IQ scores.
But alcohol was a different story. "In particular alcohol use was found to be strongly associated with IQ decline," the study's author's wrote, reports Christopher Ingraham at The Washington Post. "No other factors were found to be predictive of IQ change."
"This is a potentially important public health message -- the belief that cannabis is particularly harmful may detract focus from and awareness of other potentially harmful behaviors," noted the study's lead author, Claire Mokrysz.
"The current focus on the alleged harms of cannabis may be obscuring the fact that its use is often correlated with that of even more freely available drugs and possibly lifestyle factors," agreed reviewer Guy Goodwin of Oxford University. "These may be as or more important than cannabis itself."
A 2012 Duke University study of just 38 subjects had made world headlines when it claimed to find a link between heavy marijuana use and IQ decline among teens. Columbia University's Carl Hart noted the very small sample of heavy users in the study led him to question how relevant were the results.