Canadian OxyContin prescriptions in Windsor rose substantially following the introduction of a tamper-resistant formulation in the United States a new report says.

Research was also conducted in Sarnia and Niagara Falls but numbers remained largely unchanged during the 14-month study period.

In August 2010, a tamper-resistant formulation of controlled-release oxycodone (OxyContin-OP) was introduced in the United States but not in Canada.

Research conducted at the Institute for Clinical Evaluative Sciences (ICES) found a 390 per cent increase in OxyContin dispensing from pharmacies close to the Detroit-Windsor Tunnel alone.

According to the report, the rate of dispensing at 14 pharmacies near the Detroit-Windsor Tunnel increased roughly four-fold between August 2010 and February 2011. The number of tablets dispensed rose from 505 to 1,969 tablets per 1,000 people during that time.

By April 2011, following warnings to prescribers and pharmacies regarding drug-seeking behaviour, the dispensing rate declined to 1,683 tablets per 1,000 people.

And by November 2011, the rate had returned to levels observed in early 2010.

The report suggests that 242,075 excess OxyContin tablets were dispensed near the Detroit-Windsor Tunnel during a 14-month span.

"There is only one plausible explanation for this finding, and it’s the diversion of huge quantities of the original OxyContin formulation from Ontario into the United States," the report’s co-author Dr. David Juurlink said in a media release.

According to the U.S. Department of Justice, Michigan and New York are both identified as "high-intensity drug trafficking areas." The department also said the epicentre of the Michigan drug trafficking is Detroit, which serves as the primary distribution centre for the region.

"The observation that increased dispensing of Oxy-Contin was limited to the region around the Detroit-Windsor Tunnel warrants discussion," the report said.

Across town, near the Ambassador Bridge, the city’s other international crossing, there was virtually no change at 12 pharmacies there.

"It is more difficult to explain the differences in OxyContin dispensing patterns between the areas surrounding the Detroit-Windsor Tunnel and the Ambassador Bridge," the report states. "It is possible that our findings are related to drug trafficking and transportation patterns in the Detroit area and that a small number of individuals were responsible for the large increase in dispensing on the Canadian side of the tunnel."

Windsor Police spokesperson Sgt. Matthew D’Asti read the report and consulted with the department’s drug squad. He’s not sure what to make of the report. Although, he said criminal activity "is certainly possible."

"There are so many variables in the report. Are you dealing with doctors over-prescribing OxyContin or are you dealing with forged prescriptions?" D’Asti asked. "What is the report saying? If there is a criminal element, is it forged prescriptions?"

According to the researchers, the College of Physicians and Surgeons of Ontario sent a notice to Windsor-area physicians in March 2011 warning of potential drug-seeking behaviour. In April 2011, the Ontario College of Pharmacists posted a similar alert on its website, researchers said.

More recently, the Ontario College of Pharmacists released a statement.  It "urges members [of the College] to remain vigilant for situations when American residents are seeking to fill OxyContin prescriptions from U.S. based prescribers who are also licensed in Ontario."

The statement went further, saying, "as always, members should also remain vigilant for fraudulent prescriptions, especially those written for the higher strengths of OxyContin tablets."

A call to the College of Physicians and Surgeons of Ontario wasn't immediately returned.