The reason intelligent people tend to do more drugs, according to a study, is that more intelligent people are "more likely to engage in evolutionary novel behavior." Psychoactive drugs like cocaine (first made in 1860) and heroin (1874) are relatively new and therefore qualify as novel behavior--at least looking at the long evolutionary clock. If you indulge and see this as justification, be advised that there are also ample studies that show intelligent people often do very stupid things.
You might protest that some of the dumbest people you've ever met drink and drug like the fools they are--and that's all true. Drug taking is hardly the exclusive domain of bright minds. But as Psychology Today points out: "A National Child Development Study shows that more intelligent children in the United Kingdom are more likely to grow up to consume psychoactive drugs than less intelligent children." Also: "'Very bright' individuals (with IQs above 125) are roughly three-tenths of a standard deviation more likely to consume psychoactive drugs than 'very dull' individuals (with IQs below 75)." That could always be because the intelligent types run into more dealers than the "very dull."
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