A new study finds that OxyContin abuse has decreased now that the painkiller has been reformulated to make it more difficult to misuse.

Many people who abused the drug have switched to heroin, the researchers report in the New England Journal of Medicine. The study included more than 2,500 people who were dependent on opioids, who were followed between July 2009 and March 2012. During that time, there was a 17 percent decrease in OxyContin abuse. In 2010, the company that makes OxyContin introduced a new version of the drug that is more difficult to inhale or inject.

During the same period, heroin abuse doubled, ABC News reports.

"I think the message we have to take away from this is that there are both anticipated consequences and unanticipated consequences to these new formulas," lead researcher Theodore Cicero of Washington University in St. Louis said. "Substance abuse is like a balloon: If you press in one spot, it bulges in another."

The study found almost one-fourth of participants were able to abuse OxyContin despite the reformulation, and 66 percent switched to heroin. The article notes that a small bag of heroin can cost as little as $5, compared with an 80-milligram dose of OxyContin, which can cost up to $80 on the street.

"Our data show that an abuse-deterrent formulation successfully reduced abuse of a specific drug but also generated an unanticipated outcome: replacement of the abuse-deterrent formulation with alternative opioid medications and heroin, a drug that may pose a much greater overall risk to public health than OxyContin," the researchers wrote. "Thus, abuse-deterrent formulations may not be the 'magic bullets' that many hoped they would be in solving the growing problem of opioid abuse."

USA Today reported recently that misuse of the opioid Opana has increased since OxyContin was reformulated.

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