In Vietnam, the water buffalo have always shunned the local opium plants. They don’t like them. But when the American bombs started to fall all around them during the war, the buffalo left their normal grazing grounds, broke into the opium fields, and began to chew. They would then look a little dizzy and dulled. When they were traumatized, it seems, they wanted — like the mongoose, like us — to escape from their thoughts.

Some drug use causes horrible harm, as I know very well, but the overwhelming majority of people who use prohibited drugs do it because they get something good out of it — a fun night out dancing, the ability to meet a deadline, the chance of a good night’s sleep, or insights into parts of their brain they couldn’t get to on their own. For them, it’s a positive experience, one that makes their lives better. That’s why so many of them choose it. They are not suffering from false consciousness, or hubris. They don’t need to be stopped from harming themselves, because they are not harming themselves. As the American writer Nick Gillespie puts it: “Far from our drugs controlling us, by and large we control our drugs; as with alcohol, the primary motivation is to enjoy ourselves, not to destroy ourselves . . . There is such a thing as responsible drug use, and it is the norm, not the exception.”

So, although it is against my instincts, I realized I couldn’t give an honest account of drug use in this book if I talked only about the harm it causes. If I’m serious about this subject, I also have to look at how drug use is deeply widespread — and mostly positive.