"While most Americans still consider it plausible that LSD causes insanity," I wrote in my 2003 book Saying Yes, "they would probably be surprised, if not amused, to hear that the same charge was once leveled against marijuana." Make that "is now being leveled." As The Drug War Chronicle notes, the Office of National Drug Control Policy has revived the quaint claim that smoking pot drives you crazy, based on a few studies that found an association (though not necessarily a cause-and-effect relationship) between early and/or heavy marijuana use and subsequent mental problems.
I'm not sure about most Americans, but I confess that I am a bit surprised that reefer madness has made a comeback, given the lineage of this much-ridiculed claim. It's as if anti-drug warnings are on a loop, and insanity has come around again. I suppose we should expect lurid tales of marijuana murders in a few years.