“Heroin has a frightening reputation, and rightly so: the margin between an effective dose and an overdose is narrower than that of any other mainstream narcotic. A paper in Addiction, an academic journal, estimated the quantity of various drugs needed to get an average person high versus the amount required to kill them.5 In the case of alcohol, it found that the ratio was about ten to one—in other words, if a couple of shots of vodka are enough to make you tipsy, twenty shots might kill you, if you can keep them down. Cocaine, it found, was slightly safer, with a ratio of fifteen to one. LSD has a ratio of 1,000 to one, whereas marijuana is safest of all: it is impossible to die of overdose, as far as anyone can tell. Even with the edibles, there is no evidence that one can die of overdose—you simply have a stronger and longer-lasting effect than you may have wanted. For heroin, the ratio between an effective dose and a deadly one is just six to one. Given that batches vary dramatically in their purity, each shot is a game of Russian roulette. Dealers”