But starting in the 1990s, there has been a vast expansion in the long-term use of opioid painkillers to treat chronic nonmalignant medical conditions, like low-back pain, sciatica and various musculoskeletal problems. To no small degree, this change in clinical practice was encouraged through aggressive marketing by drug companies that made new and powerful opioids, like OxyContin, an extended-release form of oxycodone that was approved for use in 1995.

The pitch to doctors seemed sensible and seductive: Be proactive with pain and treat it aggressively. After all, doctors have frequently been accused of being insensitive to pain or undertreating it. Here was the corrective, and who in their right mind would argue that physicians shouldn’t try to relieve pain whenever possible?

Well, doctors clearly got the message: The medical use of these drugs grew tenfold in just 20 years. Nearly half of all prescriptions by pain specialists are for opioids. But strikingly, primary care physicians, who generally do not have any particular expertise or training in pain management, prescribed far more opioids overall than pain specialists. For example, in 2012, 18 percent of all prescriptions for opioid analgesics were written by family practitioners, and 15 percent by internists, compared to 5 percent for pain specialists. (This partly reflects the fact that there are fewer pain specialists than primary care doctors.)

The consequences of this epidemic have been staggering. Opioids are reported in 39 percent of all emergency room visits for nonmedical drug use. They are highly addictive and can produce significant depressive and anxiety states. And the annual direct health care costs of opioid users has been estimated to be more than eight times that of nonusers.

But most surprising — and disturbing — of all is that there is actually very weak evidence that opioids are safe or effective for the long-term treatment of nonmalignant pain. So how did they become so popular for these uses? A large review article conducted between 1983 and 2012 found that only 25 of these were randomized controlled trials and only one study lasted three months or longer. The review concluded that there was little good evidence to support the safety or efficacy of long-term opioid therapy for nonmalignant pain. (In contrast, there is little question that opioid analgesics are highly effective for the relief of short-term pain.)