Does weekly marijuana use by teens really cause a drop in IQ?

A new study suggests marijuana use could have an impact on America's IQ, but how great is the effect?
Maia Szalavitz
Time Magazine (US)
Tuesday, August 28, 2012

Heavy marijuana use is associated with cognitive decline in about 5% of teens, according to a new study, which suggests that the heaviest users could lose 8 IQ points, according to a report, published in the Proceedings of the National Academy of Sciences. If the link is real, the effects on cognition could be dramatic. But intelligence and cognition is affected by a plethora of other factors, including genetic, social and environmental influences that may supersede any influence from drug use.