Compared to some of the drugs out there, cannabis can seem relatively harmless. It doesn't have the ruinous effects of methamphetamines or even substances like synthetic pot
. But there has long been suspicion that heavy use might have long-term effects on IQ, for instance [pdf
]. Factors that tend to accompany cannabis consumption, such as the use of other drugs and alcohol and, in adolescents, a tendency to skip class, have made it difficult to decisively pin a dip in IQ to marijuana use. To clear away the noise, the authors of a new study in the Proceedings of the National Academy of Sciences
turned to the reams of data from the Dunedin Multidisciplinary Health and Development Study
, and they've found that on average, by the time they reached age 38, heavy pot users diagnosed with cannabis dependence during adolescence suffered an 8-point drop in IQ. In the ...
