In 2010, a dentist extracted my wisdom teeth, told me to gargle with salt water, and sent me home with a prescription for a Costco-sized bottle of hydrocodone pills. During the procedure, she knocked me out with propofol—the same drug that killed Michael Jackson—and afterward I felt no pain. After a few hours, I popped one hydrocodone, more out of politeness than need. Weeks later, I still felt fine, but I popped two more, just to see what it was like. Hydrocodone’s dreamy, pain-dulling effect was impressive: I bit my cheek hard enough to draw blood, and it didn’t hurt at all. But the pills made me woozy. I then put the remaining 57 or so of them into my medicine cabinet, and I have no idea what happened to them after that. Lost in a move, I guess.

Heroin epidemics don’t come and go randomly, like the McRib. They have clearly identifiable causes—and in this case, by far the largest cause is doctor-prescribed pills. Every year since 2007, doctors have written more than 200 million prescriptions for opioid painkillers. (Consider that there are 240 million adults in the country.) And about four in five new heroin addicts report that they got addicted to prescription pills before they ever took heroin.

My experience was typical: Most people who try opiates don’t get addicted. But enough do. Since 2002, the total number of monthly heroin abusers has doubled to 335,000 nationwide. Some of the addicts get the pills through a well-meaning doctor or dentist, and many others swipe leftover pills from their friends or family members. The result for an addict is the same: Once the pills or money run out, heroin is still available—and cheap. At about $10 per hit, it can be half the street cost of pills.

“We seeded the population with opiates,” says Robert DuPont, an addiction doctor who served as drug czar under Presidents Nixon and Ford and who is now a harsh critic of opiate over-prescription. The supply shock from easy access to prescription drugs has pushed heroin use out of cities and into rural and suburban and middle-class areas. Massachusetts reported a staggering 185 heroin deaths outside its major cities since November, and Peter Shumlin, the governor of Vermont, spent his entire “state-of-the-state” address talking about the nearly eightfold increase in people seeking opiate treatment there since 2000. “What started as an OxyContin and prescription-drug addiction problem in Vermont has now grown into a full-blown heroin crisis,” he said.

Just 30 years ago, the pills were barely available in the United States, and the only way to get addicted to opiates was to shoot or snort heroin, probably bought on a street corner from a man carrying a weapon. DuPont observed a heroin boom in the late ’60s in Washington, D.C., when users consisted primarily of young black men with criminal backgrounds. Dupont says these users chose heroin as their first drug, skipping more benign highs like marijuana. That wave gained energy when American servicemen began returning from Vietnam, where pure Golden Triangle heroin—the granddaddy of all smack—could be bought cheap. “Through 1992, if you went to a methadone program, that’s who you’d see,” DuPont says. “It was an aging population of people who began their addiction in the 1970s.”