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Prescription painkiller OxyContin, which will be delisted from Ontario's drug benefit program.Michelle Siu For The Globe and Mail

Patients who are prescribed opioids within a week of minor surgery are at risk of becoming chronic users, according to a Canadian study published Monday.

Researchers say tailored post-operative plans are needed to make sure patients aren't being given painkillers that they don't need or ones that are too strong.

Some 391,139 Ontario patients were studied by researchers from the Institute for Clinical Evaluative Sciences and St. Michael's Hospital. All were 66 or older and had low-pain operations, such as for cataracts, gallbladder removal, prostate tissue removal or varicose vein stripping.

Within a week of surgery, 7 per cent were given opioids, including codeine and oxycodone – the generic name for OxyContin – according to the study. One year later, more than 10 per cent of them were continuing to use the medications.

"We think part of the reasoning behind these things occurring is because there are standardized templates for discharge from hospital," said Chaim Bell, the senior researcher of the study, which was published in the Archives of Internal Medicine.

"[The templates]are not well tailored to some of the patients that may not need pain medications."

There are high rates of addiction to opiods, powerful narcotic painkillers, across Canada. One popular form, OxyContin, is being limited by many provinces to curb addiction.

The study also found that many patients who initially took low-potency opioids began taking more potent ones within a year. Long-term use can lead to addiction and increased tolerance.

A standardized dose is often prescribed regardless of anticipated post-operative pain, the study says. Dr. Bell said improved communication between the surgeon and primary care provider would help to assess anticipated pain level and duration, so that the right prescription is given.

Dr. Bell said the study examines elderly patients because they are covered by the provincial drug benefit plan, so a database of prescriptions is available. But he said the findings likely suggest that all age groups are being prescribed drugs that they might not need, exposing them to the risk of chronic use or addiction.

"I do think that the basic concept applies," he said, "that we need to better tailor the pain control or the pain treatment post-operatively."

Mel Kahan, an addiction expert with the University of Toronto's family medicine department, said that while the study's results aren't surprising, it reaffirms that doctors need to prescribe opioids more carefully.

"They do have potential risks and they need to be prescribed more carefully, especially in the long-term," Dr. Kahan said.