But the reformulation, introduced in August 2010 to make it harder to crush the medicine into powder, limiting the ability to snort, inject or smoke it, may be causing other problems, researchers warn.

Interviewed recently, only about 13 percent of addicts with an opioid dependence said it was their primary drug of abuse, compared to about 36 percent prior to the new version hitting the shelves.

But the researchers also found that addicts are simply shifting to other drugs, particularly heroin, after the reformulation by the manufacturer, Purdue Pharma.

"They didn't stop (abusing drugs). They turned to something else," said Theodore Cicero of Washington University in St. Louis, first author of a letter in the New England Journal of Medicine detailing the results. "We should have asked the question, 'If they stop using the most popular drug out there, what are they going to turn to now?'"

After the reformulation, heroin use doubled. That accounted for nearly all of the increase in the use of opioids other than OxyContin (including high-potency fentanyl and hydromorphone) which jumped from about 20 percent to about 32 percent.

"They drift into more potentially-dangerous drugs like heroin," Dr. Edward Michna, a pain expert at Brigham and Women's Hospital in Boston, told Reuters Health.

Cicero said that when the drug first came out, OxyContin "was advertised by the company and the Food and Drug Administration (FDA) as having a very low abuse potential" because it was slow-release formula.

"What they didn't take into account was that the pill was pretty easy to crush," allowing addicts to snort or inject it to get an immediate rush, Cicero told Reuters Health.

The new formulation becomes a harder-to-manage gel when put in water, or becomes too chunky to snort easily when crushed.

MANY SWITCH TO HEROIN

Cicero and his colleagues gathered their new data from anonymous surveys of more than 2,500 addicts. In addition, 103 agreed to be interviewed, online or by telephone. "These abusers are all pretty hard core," he said.

There are ways to get around the tamper-resistant reformulation, about a quarter reportedly did. Yet "a lot of work is entailed in doing that," said Cicero.

Two-thirds "indicated a switch to another opioid, with 'heroin' the most common response," the researchers reported.

The jump in heroin use came in the second quarter of 2011, six months after OxyContin use began a long slide.

"The most amazing thing was how quickly it dropped because they weren't able to extract the drug anymore. They switched to drugs that were potentially more harmful to them." said Cicero.

The researchers quoted one respondent as saying, "Most people that I know don't use OxyContin to get high anymore. They have moved on to heroin (because) it is easier to use, much cheaper, and easily available."

Heroin is more worrisome because intravenous use increases the risk of HIV and hepatitis, and the heroin is often cut with dangerous chemicals, said Cicero.

"Thus, abuse-deterrent formulations may not be the 'magic bullets' that many hoped they would be in solving the growing problem of opioid abuse," he and his team concluded.

DRUG ABUSE ‘LIKE A BALLOON'

In May, another group of researchers reported a similar decline based on 11 months of post-reformulation data from patients in 324 centers throughout the U.S.

That study assessed the experience of patients during the first 11 months after introduction of the new tablets. It found that before the reformulation, about a quarter of people abusing prescription opioids were doing it with OxyContin. The rate subsequently fell to about one in eight.

According to that study, led by Dr. Ryan Black of Inflexxion Inc., in Newton, Mass., those reporting that they snorted, injected or smoked the drug fell to 5 percent. It had been 18 percent. But the rate of oxymorphone abuse more than doubled, going from about two percent to four-and-a-half percent.

"We need to look at the demand side" when dealing with the problem, said Cicero. "Drug abuse is like a balloon. If you crush one side of the balloon, the volume doesn't go away, it just pops out somewhere else."

"The problem is substance abuse. It's not the drug. It's not the formulation," said Michna, who was not involved in the new study. "I think our energy should be dedicated toward the disease of addiction, educating physicians on the disease of addiction, focusing more money on research and treatments rather than putting money into expensive formulations that probably won't achieve much."

SOURCE: bit.ly/ORiJss New England Journal of Medicine, July 12, 2012.

• A Permanent Economic Emergency