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Despite the risk of overdose and addiction, many Canadians are being prescribed powerful opioid painkillers in dosages that exceed clinical guidelines, leading to an increased risk of death, a study has found.

People 15 to 64 years old who were prescribed high doses of opioids, such as oxycodone, codeine and morphine, were nearly three times more likely to die of opioid-related causes than those prescribed lower doses, according to a study published on Monday in the Archives of Internal Medicine.

The findings, based on Ontario data, add to growing evidence that opioids are being overprescribed and misused among patients with chronic non-cancer pain, according to Tara Gomes, lead author of the study and project research lead of the Ontario Drug Policy Research Network, based at the Institute for Clinical Evaluative Sciences in Toronto.

"I think that physicians need to really increase their awareness of the dangers associated with these drugs and consider that when deciding whether to start a patient on an opioid," she said. "In my opinion, patients also need to be made aware when they are being prescribed this medication of the risks associated with their prescription and the fact that perhaps there are other treatment options for their pain."

People who had been diagnosed with cancer or those in palliative care were excluded from the study.

The use of powerful opioids to treat chronic pain not related to cancer has become a flashpoint in the medical community as some medical experts say they carry serious risks that patients and even doctors underestimate, while others defend their use as an important pain-treatment tool. Some of the most outspoken proponents of opioid use to treat chronic pain have ties to companies such as Purdue Pharma, which sells the brand-name opioid drug OxyContin.

The Canadian Pain Society, an advocacy group, issued a press release last month criticizing another study by Ms. Gomes and her colleagues that suggested some Ontario family doctors prescribe significantly higher amounts of opioid drugs than others. The society defends the use of opioid drugs and says research emphasizing the harms is often flawed or misleading.

But the news release does not mention that the Canadian Pain Society is linked to drug companies that sell opioid painkillers. For instance, the society jointly funds an education award with Purdue Pharma and has accepted sponsorship money from Purdue.

Roman Jovey, a pain specialist and member of the society, said drug-company money is used to directly help patients. He says opioids aren't perfect, but are often the only option for many, particularly those with low incomes, who don't qualify for coverage of physiotherapy or other alternatives. More work is needed to address the area of chronic pain, Dr. Jovey said.

In the study, researchers examined data from more than 607,000 patients aged 15 to 64 who were eligible for provincial drug coverage and received an opioid painkiller prescription in the period from Aug. 1, 1997, to Dec. 31, 2006.

During that time, a total of 1,463 people died from causes related to opioid drugs, according to coroner reports. Researchers then excluded hundreds of those deaths because they wanted to focus only on those deaths where the individual had recently received a prescription for an opioid drug.

They compared 498 individuals who had died while taking opioids to a control group consisting of individuals who were taking opioids but did not die during the study period. The researchers found that patients who took opioids in doses higher than 200 milligrams a day, the maximum recommended in medical guidelines, were nearly three times more likely to die of opioid-related causes than those given lower doses.

Researchers also found that those who died from opioid-related causes were likely to be taking more than one opioid drug or be taking tranquillizing drugs known as benzodiazepines. Many of them were also likely to have a history of abusing alcohol or obtaining opioid drugs from multiple doctors and pharmacies.

Those who died also tended to be in low-income brackets.

Ms. Gomes said a significant part of the problem is the fact that chronic pain is a challenge to treat and many patients may not have access to specialist services that can offer alternatives to powerful drugs, such as physiotherapy, acupuncture or non-opioid painkillers.

"Pain is a major condition in Canada and elsewhere all around the world right now," she said. "We don't have a good enough understanding of how to treat it properly and how to make sure that people are receiving the appropriate treatment that is safe and effective."