In 2007, 373,000 Americans reported using heroin in the previous year.

Four years later, that figure was 620,000. Drug overdoses, the vast majority involving opiates, are killing more people every year than automobile accidents among certain age groups. So why is junk taking over the land of the free?

That's the question Sam Quinones sets out to answer in this engrossing, often disconcerting journey through the parallel worlds of America's opiate epidemic. The former LA Times reporter weaves an engaging, if meandering narrative, taking in a host of characters and locations, predominantly in the once thriving small industrial cities of the Rustbelt and the wild ranchos south of the border.

From the tiny Mexican state of Nayarit, 180 miles of Pacific Ocean coastline rising to the Sierra Madre Mountains, come the Xalisco boys. Arguably the world's most successful heroin distribution network, these farmhands-cum-drug dealers moved north in the late 1980s, taking with them a particularly noxious brand of semi-processed heroin known as "Black Tar". Operating as quasi-autonomous cells, delivering drugs "like pizza", the Xalisco boys' cheap heroin flooded into vast swathes of suburban America, from California and New Mexico to Ohio and Colorado. Towns that had barely seen a junkie before were, by the turn of the millennium, witnessing a wave of drug deaths.

But the Mexican connection is only one part of Quinones's story - and arguably not the pivotal one. Opium is not a modern analgesic. Mesopotamians grew poppies by the banks of the Tigris and the Euphrates. For almost as long pharmacists have searched for the "Holy Grail", a non-addictive treatment for chronic pain. Then, in 1996, Purdue Pharma, a small pharmaceutical outfit, told the world they had found it: a slow release, opiate-based pill named OxyContin.

A rapidly growing legion of pharmaceutical salespeople billed OxyContin as a risk-free wonder drug. Purdue offered free coupons to doctors that could be exchanged. By the time the scheme was discontinued, 34,000 free prescriptions had been redeemed. In a court case in 2007 Purdue pleaded guilty to misbranding the drug "with intent to defraud and mislead the public". But while Purdue has faced attempts to make the company legally liable for the effects of addiction, there has been no court finding against them.

OxyContin users were not just patients with terminal illnesses or chronic pain. Pills were given to almost anyone who crossed the surgery door with a complaint. Addicts soon began crushing tablets and injecting them. And once they could no longer afford the pills, OxyContin addicts turned to the nearest and cheapest substitute, black tar heroin.

One addiction specialist tells Quinones he never meet a heroin addict who didn't start on OxyContin, often indirectly led to the drug by Purdue Pharma's aggressive marketing. "They wouldn't be selling this quantity of heroin on the street right now if they hadn't made these decisions in the boardroom."

The similarities between the business models of the heroin peddler and the pharmaceutical giants are uncanny. The Xalisco boys operated a "just-in-time" system. Pick up a phone, dial a number and within minutes one of a fleet of delivery drivers, balloons filled with tiny quantities of Black Tar heroin pressed hard against their gums, would be at your door. Dealers were salaried, never used drugs, didn't carry guns or fraternize with their clients. The service was clean, fast and, crucially, convenient.

The conveyor belt of pills was little different. "Pill mills", virtual ATMs for dope staffed by a doctor with a prescription pad and no desire to ask questions, set up in small towns and minor cities, swamping suburban America. In places, pills became ersatz currency; food, clothes, even washing machines and dishwashers all carried OxyContin price tags.

Dreamland could use an editor; the myriad characters and stories, typically delivered in sections of only a few pages, too often bleed into one another. But the cumulative affect is powerful nonetheless. We meet Russian Pentecostals who escaped persecution in the Soviet Union only to find their children enslaved to the needle. There is the star quarterback who is given OxyContin to treat pain after an injury on the football field. Two years later, he is dead of a heroin overdose.

So why has a generation born into unparalleled affluence taken up the most notorious drug habit of all?

That question cannot be answered by cheap dope and plentiful pills alone. But Quinones has his theories. Many of the small cities he frequents are in the midst of a political, social and economic breakdown that New Yorker writer George Packer dubbed "the great unwinding". The titular Dreamland is illustrative. Dreamland, a massive outdoor swimming complex, was once the hub of the industrious Ohio city of Portsmouth. Industry left Portsmouth from the 1960s on. Dreamland closed in 1993. Heroin appealed to the blank generation left behind; "to the suburban kids hooked first on pills, heroin fulfilled the dream of the adventures they'd never had in their quiet towns."

America is waking up to the scale of its opiate epidemic. Last year, the death of actor Philip Seymour Hoffman, discovered in his New York apartment surrounded by bags of heroin branded with Ace of Spades insignia, sent shockwaves. In 2010, Purdue reformulated OxyContin to make it more difficult to abuse. But the damage has been done. The pills have produced a new generation of junkies. A tenth of Baltimore is addicted to heroin, according to the Drug Enforcement Agency.

Quinones, to his credit, tries to see the positives amid the pain. Parents are less afraid to speak out. Faced with phalanx of white, middle-class heroin addicts, Republicans in conservative states have softened their stance on drugs. Scientific knowledge of how addiction works has been transformed. Portsmouth, Ohio has become a centre for addiction treatment.

But there is little comfort in any of this, either in America or closer to home. The spent blister packets discarded on our city streets attests to Scotland's own silent epidemic. Opiate-based prescriptions have increased almost 60 per cent in five years. Our own dreamland may not be too far away.

Dreamland: The True Tale of America's Opiate Epidemic, by Sam Quinones, is published by Bloomsbury, £18.99