How did America get to a point where legal opioid painkillers, marketed as medicine, were involved in nearly 19,000 overdose deaths in 2014?

One alarming explanation: The drug companies behind these opioids wanted more people to buy their product, so they led a misleading campaign to get doctors to prescribe their drugs.

The result: Drug companies profited as more and more people got addicted and died of overdoses. This chart, from a 2015 study published in the Annual Review of Public Health, tells the story:

Let's back up. The opioid epidemic began in the 1990s when doctors prescribed a tremendous amount of opioid painkillers to help treat pain — a serious problem, given that chronic pain alone afflicts about 100 million Americans.

But one reason doctors were so willing to prescribe these painkillers, despite the clear risks of addiction and overdose, is heavy marketing from the pharmaceutical industry.

Andrew Kolodny and other public health experts explained the history in the Annual Review of Public Health, detailing Purdue Pharma's involvement after it put OxyContin on the market in the 1990s:

Between 1996 and 2002, Purdue Pharma funded more than 20,000 pain-related educational programs through direct sponsorship or financial grants and launched a multifaceted campaign to encourage long-term use of [opioid painkillers] for chronic non-cancer pain. As part of this campaign, Purdue provided financial support to the American Pain Society, the American Academy of Pain Medicine, the Federation of State Medical Boards, the Joint Commission, pain patient groups, and other organizations. In turn, these groups all advocated for more aggressive identification and treatment of pain, especially use of [opioid painkillers].

Often, these campaigns propagated highly misleading claims. Such as claims that OxyContin and other new opioid painkillers were safer than other medications on the market — as we're now seeing, they aren't. Or assertions that opioid painkillers can treat chronic pain — in reality, the evidence for opioids treating long-term, chronic pain is very weak, despite their effectiveness for acute, short-term pain.

The claims were so misleading, in fact, that Purdue Pharma eventually paid hundreds of millions of dollars in fines for them. The Associated Press reported in 2007:

Purdue Pharma, its president, top lawyer and former chief medical officer will pay $634.5 million in fines for claiming the drug was less addictive and less subject to abuse than other pain medications, U.S. Attorney John Brownlee said in a news release.… Purdue learned from focus groups with physicians in 1995 that doctors were worried about the abuse potential of OxyContin. The company then gave false information to its sales representatives that the drug had less potential for addiction and abuse than other painkillers, the U.S. attorney said.

But in the midst of the misinformation campaigns, doctors prescribed hundreds of millions of prescriptions for opioids — in 2012, enough to give a bottle of pills to every adult in the country. And as people became addicted to opioid painkillers, they also began turning to a cheaper, more potent opioids — such as heroin and fentanyl — to satiate their cravings.

The result: In 2014, there were a record 47,000 drug overdose deaths in the US, nearly two-thirds of which were opioid-related, according to federal data. (For more on the drug epidemic, read Vox's explainer.)

Pain patients thought they were being helped, and doctors thought they were helping their patients. But really, people's lives were put in danger — largely so drug companies could make some money.