Not long ago, I was talking with a couple of friends who are about a decade younger than I am. We got onto the subject of recreational drugs and how my friends had recently sworn off Ecstasy. "I know a guy who used to love it, and he's quitting, too," one of them explained. "He's learned a lot about it and says it's just too hard on your body." I remarked that since Ecstasy is the sort of drug most people take only very occasionally, it probably wasn't as dangerous as something like cocaine, which can be addictive, expensive and lethal. "Oh, cocaine's not that bad," said my friend, looking puzzled and leaving me surprised. Hadn't he ever worked for someone who'd gotten so tweaked on coke that he burned out his septum, emptied his bank account and triggered a heart at tack? Hasn't every journalist worked with someone like that?Ryan Grim would understand this disconnect perfectly. One of the theses of his new book, This is Your Country on Drugs: The Secret History of Getting High in America-- a cornucopia of unconventional wisdom about our relationship to mind-altering substances -- is that the popularity of drugs waxes and wanes according to a complex sum of factors. One of those factors is the "perceived risk" of using a particular chemical, which also fluctuates. There's a tendency to idealize new drugs, as the Boston Medical and Surgical Journal did with a recently isolated narcotic in 1900. "There's no danger of acquiring a habit," it assured its readers about the drug that had just emerged from the labs of the aspirin manufacturer, Bayer. They named it heroin.