About that cannabis link to low IQ…

Scientific American: Pot Smokers Might Not Turn into Dopes after All

This won’t be a surprise to anyone here, but it is an important rebuttal to all the prohibitionists who have been citing the New Zealand longitudinal “Dunedin” study as proof of the harmfulness of cannabis.

Cannabis rots your brain — or does it? Last year, a paper published in Proceedings of the National Academy of Sciences (PNAS) suggested that people who used cannabis heavily as teenagers saw their IQs fall by middle age. But a study published today — also in PNAS — says that factors unrelated to cannabis use are to blame for the effect.

Prohibitionists are constantly searching for some kind of smoking gun that they can use against cannabis legalization, and so they use science not to discover the truth, but to find any kind of evidence of what they want to be true. And naturally, they find it.

This is a clear form of confirmation bias. If they took more time (and willingness) to actually study the science, in most cases they would find other possible explanations for the same results, and would also question why this didn’t show up elsewhere.

Mitch Earleywine, a psychologist at the University at Albany, State University of New York, says that Røgeberg’s analysis definitely supports the idea that links between adolescent cannabis use and drops in IQ are essentially spurious, arising from socioeconomic differences rather than any sort of pharmacological action. John Macleod of the University of Bristol, UK, who works on the ALSPAC data, points out that Meier and her colleagues acknowledged in their original paper that the results might be caused by confounding factors. He adds that the modelling in Røgeberg’s paper shows that within a set of reasonable assumptions, this is indeed possible.

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