According to a study conducted by Ontario Drug Policy Research Network, thousands of OxyContin pills dispersed in Canada ended up being smuggled into the United States during an 18 month period.
Between August 2010 and February 2012, Canada was offering the more addictive form of Oxy, while the United States was offering a tamper-resistant version of the drug that was not addictive. Researchers found that there was a large increase in the dispensing of OxyContin tablets at the Detroit-Windser tunnel area of the border between the two countries. During the time period, up to 250,000 OxyContin tablets were sold in excess than the amount needed in Canada. These pills are believed to have been smuggled into the United States for sale.
Source: Canadian Press, “Canada to heed U.S. pleas to crack down on generic OxyContin, Ambrose hints,” Global Post, October 21, 2013.