PICTURE a heroin addict. “A bum sitting under a bridge with a needle in his arm, robbing houses to feed his addiction,” is what many people might imagine, believes Cynthia Scudo. That image may have been halfway accurate when heroin first ravaged America’s inner cities in the 1960s and 1970s. But Ms Scudo, a smartly dressed young grandmother from a middle-class Denver suburb, knows that these days it is not always like that. Until not so long ago, she was a heroin addict herself.

The face of heroin use in America has changed utterly. Forty or fifty years ago heroin addicts were overwhelmingly male, disproportionately black, and very young (the average age of first use was 16). Most came from poor inner-city neighbourhoods. These days, the average user looks more like Ms Scudo. More than half are women, and 90% are white. The drug has crept into the suburbs and the middle classes. And although users are still mainly young, the age of initiation has risen: most first-timers are in their mid-20s, according to a study led by Theodore Cicero of Washington University in St Louis.

The spread of heroin to a new market of relatively affluent, suburban whites has allowed the drug to make a comeback, after decades of decline. Over the past six years the number of annual users has almost doubled, from 370,000 in 2007 to 680,000 in 2013. Heroin is still rare compared with most other drugs: cannabis, America’s favourite (still mostly illegal) high, has nearly 50 times as many users, for instance. But heroin’s resurgence means that, by some measures, it is more popular than crack cocaine, the bogeyman of the 1980s and 1990s. Its increased popularity in America contrasts strongly with Europe, where the number of users has fallen by a third in the past decade. What explains America’srelapse?

A shot in the arm

Like many of America’s new generation of users, Ms Scudo never intended to take up the drug. Her addiction began in 2000 when, after a hip injury, a doctor prescribed her “anything and everything” to relieve the pain. This included a high dose of OxyContin, a popular brand of opioid pill. Her prescription was later reduced, but she was already hooked. On the black market OxyContin pills cost $80 each, more than she could afford to cover her six-a-day habit; so she began selling her pills and using the proceeds to buy cheaper heroin. As if from nowhere, Ms Scudo had become a heroin addict.

Thousands more have gone down this path. The 1990s saw a big increase in prescriptions of opioids for chronic pain. In some states the number of opioid prescriptions written each year now exceeds the number of people. That oversupply feeds the black market: last year 11m Americans used illicitly-acquired prescription painkillers, more than the number who used cocaine, ecstasy, methamphetamine and LSD combined. People who would never dream of injecting heroin seem to assume that opioids in packets are safe. But they aren’t. In 2012 prescription painkillers accounted for 16,000 deaths—nearly four out of every ten fatal drug overdoses in America. As the toll grew, some states tightened up the law. In many places doctors must now check databases to make sure the patient has not already been prescribed painkillers by another clinic. Prescriptions have been cut down to as little as a single pill, to reduce the supply of unfinished packets. “Pill mills”, clinics that churned out prescriptions with no questions asked, have been shut down. And drug manufacturers have made their medicines harder to abuse: the latest OxyContin pills, when crushed, turn into a gloop that cannot easily be snorted or dissolved for injection.

These measures have had some impact: rates of prescription-drug abuse and of overdose have dipped a little in the past two years. But as the supply of pain pills has dropped, and their black-market price has risen, many addicts have turned to heroin to satisfy their craving more cheaply. “We saw it coming at us at 90mph, like a freight train,” says Meghan Ralston of the Drug Policy Alliance, a drug-reform pressure group. The number of deaths from heroin overdoses doubled between 2010 and 2012, and many of those attending addiction clinics are college-age, middle-class types who started on prescription pills.

The Mexican wave

Just as the demand side of America’s heroin market was heating up, so too was supply. Though Afghanistan accounts for 80% of global opium production, America gets most of its heroin from Mexico. Historically that has checked consumption, since Mexico has long been a relatively small producer of opium poppies.

In the past few years the Mexicans have upped their game. One of the many unintended consequences of Mexico’s war on organised crime in urban hotspots, such as Ciudad Juárez, was that the army was diverted from poppy eradication in the countryside. Farmers in the Sierra Madre made the most of this: by 2009 cultivation was ten times higher than in 2000. Although production has fallen back in the past few years, Mexico is now the world’s third-biggest producer of opium, after Afghanistan and Myanmar.

Policy changes in America have given Mexico’s narco-farmers further incentives to focus on opium. Until not so long ago, Mexican traffickers made a lot of their money from cannabis. But these days most of the cannabis in America is home-grown. Nearly half the states have legalised medical marijuana, and four have voted to legalise it outright. Exporting pot to the United States is now like taking tequila to Mexico. Facing a glut in the cannabis market, Mexican farmers have turned to poppies. America’s police have seen the impact. Seizures of heroin at the border with Mexico have risen from 560kg (1,230lb) in 2008 to about 2,100kg last year. And the smugglers have become bolder. “Three or four years ago, 5lb was big. Now sometimes we’re finding 20lb,” says Kevin Merrill, the assistant special agent in charge of the Drug Enforcement Administration on the outskirts of Denver. The low transport costs faced by Mexican traffickers, who need only drive from Sinaloa to the border, mean that their heroin is far cheaper than the Colombian or Asian sort. A gram of pure heroin in America now costs about $400, less than half the price, in real terms, that it cost in the 1980s. And whereas much of the heroin in the past was of the “black tar” variety, which is usually injected, there is a trend towards brown heroin, which lends itself better to snorting and smoking. That matters to novice heroin users, who may be skittish about needles. “I somehow thought that if I didn’t inject it, I wasn’t a heroin addict,” says Ms Scudo, who smoked it instead.