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David Juurlink is head of the division of clinical pharmacology and toxicology at the University of Toronto.

Over the past year I've lost track of how many times the opioid epidemic has, in one incarnation or another found its way into front-page headlines: Prince, naloxone, fentanyl, newborns in agonizing withdrawal, W-18, and so on. What distinguishes this epidemic is not only its catastrophic toll – hundreds of thousands dead, uncountable millions harmed – but also the fact that, unlike SARS, Ebola or influenza, this epidemic has no end in sight. The "why" is complex, but it relates in part to prevalent beliefs about the role of these drugs in medical practice.

It's the greatest drug safety crisis of our time, and we must face some unpleasant truths and ask some difficult questions.

One truth is that well-intentioned prescribing fuelled this crisis. For 20 years, doctors have prescribed opioids – drugs such as oxycodone, hydromorphone, fentanyl and others – liberally for chronic pain, one of the most common problems we see. We did this because the relief of suffering is our primary goal, because we are conditioned to intervene, and because we were assured on some authority that the practice was safe, effective, and based on sound medical evidence.

It's not.

Despite the best of intentions, we flooded North American homes with opioids purer and often stronger than heroin. These drugs increasingly fell into the wrong hands, destroying young lives and countless families in the process. But another unfortunate truth is that even when our patients with chronic pain took these pills as we instructed, we caused far more harm than we anticipated. Many – by some estimates, 10 per cent – spiralled into addiction, even though we had been told this would happen only rarely. Some crashed their cars. Others fell, fracturing bones or sustaining head injuries. And some, especially those prescribed high doses or who took their meds with a sedative or alcohol, simply went to sleep and didn't wake up.

Yet we continue the practice. The "why" is vastly more complicated – we've grown accustomed to it, writing a prescription is easy, pills are expected for pain, they're covered by insurance while other treatments aren't, and so on. But a critical factor is that our patients often tell us that opioids work, that they need them to function, and that they couldn't imagine facing life without them. These anecdotes, delivered honestly and with conviction, are powerful.

To openly question the role of these drugs in the treatment of chronic pain is to draw the ire of patients and, sometimes, the displeasure of colleagues, particularly those in the field of pain medicine. But it is long past time for doctors (and for that matter patients) to reflect on what happens when these drugs are prescribed for months or years at a time, and what the honest objectives of drug therapy should be.

It is true that opioids relieve pain. This is why they can be valuable after a fracture or a major operation. But it is also true that analgesia wanes with time, a phenomenon known as tolerance. As pain resurfaces, doses are often then increased, and the cycle continues. An even more pernicious phenomenon is physical dependence, which develops within days and results in withdrawal symptoms (including pain, abdominal cramping, irritability and drug craving) when opioids are stopped. Patients quickly learn that these symptoms abate when the drug is resumed. Is it any wonder that a patient with chronic pain would construe this as effectiveness? Of course not, and it's a recipe for self-perpetuating therapy.

Let's reflect for a moment on why doctors prescribe medications. The goal is always to afford benefits in excess of harms. Regardless of drug or patient, a benefit is never guaranteed, and harms always loom. This is why no self-respecting physician prescribes antibiotics for the common cold. Even in the face of minimal risk, there is no conceivable benefit because viruses do not respond to antibiotics. This is an easy calculus.

But what happens when the benefits of a drug decline with time, yet the harms persist or even increase? What if the benefits come to be defined by avoidance of withdrawal symptoms, including pain itself, thereby clouding the assessment of effectiveness? What if patients resist this concept, as they often emphatically do? And what if, unlike most other medicines, it isn't possible to simply stop treatment without triggering a cascade of new and very serious problems?

These questions bear reflection by every physician who treats chronic pain and the patients who suffer from it. The goal of opioid therapy is not simply pain relief. Like every other drug, the goal is to help more than harm. Sometimes, chronic opioid therapy meets this objective, but it does so far less often than we think.