PNAS study Here s a good review in Nature of the debate over whether cannabis causes a decline in IQ or is just associated with a decline in IQ Nature News Explainer Pot smokers might not turn into dopes after all Revisiting data casts doubts on link between heavy cannabis use and declining IQ Arran Frood 14 January 2013 Last year a paper published in Proceedings of the National Academy of Sciences PNAS 1 suggested that people who used cannabis heavily as teenagers saw their IQs fall by middle age But a study published today2 also in PNAS says that factors unrelated to cannabis use are to blame for the effect Ole R geberg a labour economist at the Ragnar Frisch Centre for Economic Research in Oslo and the author of the latest paper ran simulations which showed that confounding factors associated with socioeconomic status could explain the earlier result For example poorer people have reduced access to schooling irrespective of cannabis use Past research on the Dunedin cohort shows3 that individuals from backgrounds with low socioeconomic status are more likely than others to begin smoking cannabis during adolescence and are more likely to progress from use to dependence R geberg says that these effects combined with reduced access to schooling can generate a correlation between cannabis use and IQ change This should be included per WP NPOV If factors unrelated to cannabis are the cause then the cohort study Meier 2012 would undue weight Refs ABSTRACT mainstream media CBS