Reformulating OxyContin to make it less abusable has led drug users to switch to other opioids, particularly heroin, a survey showed.

OxyContin abuse fell significantly after the abuse-resistant version was introduced 2 years ago, but use of other opioids -- including fentanyl (Duragesic), hydromorphone (Dilaudid), oxymorphone (Opana), and heroin -- jumped from about 20% to 32% (P=0.005), according to Theodore Cicero, PhD, of Washington University in St. Louis, and colleagues.

"Abuse-deterrent formulations may not be the 'magic bullets' that many hoped they would be in solving the growing problem of opioid abuse," they wrote in a letter in the July 12 issue of the New England Journal of Medicine.

The new version of OxyContin -- harder to crush, chew, or dissolve -- entered the market in August 2010.

Between July 2009 and March 2012 the researchers surveyed 2,566 patients who were opioid-dependent but were entering a treatment program.

About 100 of these patients also gave personal interviews for further information about abuse patterns.

The researchers found the percentage of patients using OxyContin as their drug of choice fell from 35.6% before the new formulation was introduced to 12.8% almost 2 years later (P<0.001).

But primary abuse of other powerful opioids such as fentanyl, hydromorphone, oxymorphone, and heroin rose markedly during that time, from 20.1% to 32.3% (P=0.005), they found.

Indeed, clinicians and law enforcement officials now consider oxymorphone abuse a bigger problem than OxyContin abuse.

Cicero and colleagues found that abuse of hydrocodone (Vicodin) and other oxycodone products also rose slightly, but not anywhere near as steeply as the other, more powerful opioids.

OxyContin use also fell when patients were asked what opioids were used to get high in the past 30 days at least once -- from 47.4% before the introduction of the new formulation to 30% afterwards (P<0.001).

Again, users simply appeared to switch opioids, with heroin use nearly doubling during that time, they reported.

Almost a quarter of drug users (24%) said they found a way around the tamper-resistant mechanism in OxyContin, but the vast majority (66%) said they just switched to another opioid instead.

While the abuse-deterrent OxyContin "successfully reduced the abuse of a specific drug," the researchers wrote, it also "generated an unanticipated outcome:" that users simply switch to other opioids.

That's a concern not only because it doesn't do anything to stop the current opioid addiction epidemic, they said, but also because more powerful drugs such as heroin, which can put patients at greater risk of complications such as respiratory depression, can pose an even greater public health risk.