One of the more recent headlines involving
cannabis use is that it will lead over time to a substantially
lower IQ. As usual, I have looked for the actual research rather
than the sensationalistic headlines, and the studies below illustrate
many of the subtlties of statistical analysis. Also, the latest
results from a twin study, where one twin smokes and the other
doesn't, strongly suggest that long tem marijuana use is NOT the
cause of a decline in IQ.