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Morphine pills are pictured at a pharmacy in Vancouver, B.C., on Thursday October 2, 2014.DARRYL DYCK/The Globe and Mail

More than one in 10 people prescribed an opioid painkiller will remain on the drug for months and a significant number will die from an overdose, new Canadian research reveals.

One in 350 men and one in 850 women taking opioids chronically, or for three months or longer, will die as a result of the medication, according to the study, published on Thursday in the journal PLoS One.

The figures, notably for men, are "staggering," according to David Juurlink, a senior scientist at Toronto's Institute for Clinical Evaluative Sciences and lead author of the study.

"While one in 350 might not sound particularly high, remember that tens of millions of patients take these drugs and we're talking about death," Dr. Juurlink said in an e-mail. "From a public health perspective, this is a very big deal."

The study found that of all those prescribed opioids, more than 11 per cent were still taking the medication at least three months later. Among chronic users, one in 45 men and one in 70 women were eventually prescribed very high doses that are associated with a significantly increased risk of addiction and death.

It is unclear why men face much higher risks than women, but researchers say the findings highlight a need to better monitor men for dependence, addiction and death.

"I think the message for doctors is pretty clear: Think long and hard before starting a patient on long-term opioid therapy and try to avoid escalating to high doses," Dr. Juurlink said. "There are no data to suggest this represents good medical practice and you expose your patients to enormous risk if you do so."

This is the first large-scale study to quantify the risk of death among those taking opioids chronically and is significant because a high number of Canadians take opioid painkillers long-term. The study was done by looking at patient health-care records under Ontario's public drug plan. From April, 1997, to December, 2010, more than 285,000 individuals started taking an opioid drug. Of those, 32,499 were on the drugs for at least three months. The researchers followed the records of those individuals until they either stopped taking the drugs or died from any cause. They examined coroner records to determine how many deaths were caused by opioids.

The researchers said the figures in the study underestimate the actual number of opioid-related deaths because they do not take into account people who use private drug plans or obtain drugs illegally from the street.

Canada is the world's second-largest per capita consumer of opioid painkillers, a class that includes oxycodone, hydromorphone and morphine. Over the past two decades, the drugs have increasingly been prescribed to treat chronic pain. At the same time, rates of dependence, addiction and death as a result of the medication also spiked. In 2013, for instance, 513 Ontarians died as a direct result of opioids, up from 301 in 2008, according to the provincial coroner's office. Opioids can cause respiratory depression and lead people to stop breathing.

The federal and provincial governments have adopted some measures to combat prescription-drug abuse, such as cutting the reimbursement of the cost of a popular opioid under public drug plans and creating tamper-resistance requirements to make one type of opioid harder to crush or chew as a way of getting high.

But many addiction experts, such as Dr. Juurlink, say not enough is being done to address the overprescribing of these powerful, sometimes lethal, painkillers. Despite increased attention on the prescription-drug epidemic in recent years, overall opioid prescriptions jumped to 21.7 million last year, up nearly 25 per cent from 2010.

The researchers note that the findings raise important questions about how to identify people most at risk of receiving increased dosages, becoming addicted or dying from opioids. They also highlight the need for doctors to carefully consider who should receive high doses and continuously monitor and revisit those treatment plans.

Hance Clarke, director of the pain research unit at Toronto General Hospital and spokesman for the Canadian Pain Society, said chronic use of opioids is not necessarily a problem for patients in pain, especially considering that alternative treatments, such as physiotherapy, acupuncture and massage, are out of reach for most patients.

What is needed is more funding to understand what puts some people at risk and to determine how better to treat the vast numbers of Canadians experiencing chronic pain, Dr. Clarke said. "We know it's a problem. Thanks for telling us about the problem," he said. "How are we actually going to go about solving the problem?"

The study was funded by a grant from Ontario's Ministry of Health and Long-Term Care and the Institute for Clinical Evaluative Sciences.

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